Doggy deku

Chapter 1: Patience of a puppy

Chapter Text

Deku waited patiently for his master to get home, shifting on the mat in front of the door. It was four-thirty, which was the time when Kacchan usually got off work. But there were days when he had to work late, when there was a disaster or something else and people needed him.

(It wasn't really fair. Deku needed him, and Deku didn't have anything or anyone else.)

Such was the life of a dog, which was how Deku lived almost nonstop. While Kacchan went out and was a top hero, climbing the charts, Deku waited at home, dressed in his pup gear, burning time until at last his master returned to him. Considering he was a quirkless nobody, it was possibly the best post-graduation life he could have dreamed of. With mediocre marks throughout high school, there hadn't really been any point in pursuing college– not when he had that open offer from Kacchan to come live with him.

There was the click of the lock turning in the front door, and immediately Deku sprang up, dancing impatiently back and forth on all fours. The movement jostled his tail plug, sending it wagging, which was just a spiral of pleasure. All of his equipment was top-of-the-line, right down to the custom color of his fur, coordinated to match his hair. Kacchan had money to spare, and he was willing to make sure that his puppy looked the best. One of those premium upgrades was a spring-loaded tail, designed to react to Deku's body movements, often sent waving at the slightest jostle. And the more it moved, the more it nudged up inside him, making him squirm and dance on the spot. It was a never-ending cycle, and Deku spent most of the day in a haze of light arousal, every movement accompanied by a warm buzz from his prostate.

The door swung open, and Kacchan strode in, looking mildly pissed. His hero uniform stunk of smoke, which meant it had been a long day. However, upon seeing his puppy eagerly waiting for him, he managed to brighten up a little bit. After all, everyone liked seeing a dog first thing upon getting home. That was part of the point of owning one.

"What did you do all day?" Kacchan asked, kneeling down so he could scritch Deku's chin. "Knowing you, probably just pissed around on the television."

Deku whined under his breath. Kacchan was absolutely right, but it wasn't really Deku's fault. With his hands confined to mitts, there wasn't much he could do by himself. With enough patience and a little bit of trial and error, he could usually get the TV on and turn to a channel. Once in a while he would be able to drag a book down and nose it open. But a lot of it was just waiting around, being lonely for Kacchan. Not being able to engage in all the normal human stuff was frustrating, but the frustration just meant the payoff was all that much sweeter, because when Kacchan did finally come home, Deku often had his undivided attention.

Flopping to the ground, Deku rolled over and exposed his belly. This dragged a smile out of Kacchan, which Deku couldn't help but think of as a success. Years ago, he never would have imagined that he could make his old childhood bully smile like that– soft and content. Reaching out, Kacchan dragged his fingers up and down Deku's front, his fingers occasionally grazing over a nipple. This evoked more needy sounds from Deku, the man spreading his legs even wider.

Please, Deku thought, touch me already.

As always, his dick was tucked away inside its cage. Early on in living together, Kacchan had experimented with letting him roam around unconfined if he promised to be good. However, Deku hadn't been able to resist rubbing himself on things, the constant twinges from his tail sending him into a frenzy. He wanted to be a good puppy, but with no other way to occupy his time and his cock screaming for attention, he had sought relief. The result was ruined bean bag chairs, stained furniture, crusty cushions. Each time he'd been reprimanded, but as Kacchan quickly learned, reprimands reinforced behavior more than they altered them.

So the end result was that Deku stayed locked up most of the time. That didn't stop his dick from aching, often pulsing inside that cage as if begging to be let out. It rarely happened. The last time his dick had been let out was… he wasn't sure. A couple of months? It was hard to keep track of the days.

Right now, Kacchan ghosted his fingers in a slow circle around Deku's groin. The puppy whined, rolling his hips up ever-so-slightly. Even with his cock locked up, he had learned that Kacchan's fingers could get him off pretty easily. If they decided to direct their attention to his tail, playing around with it– or even better– replacimg the device with his own cock, relief would come almost instantly. Kacchan knew this, and that was why he opted for just teasing for now, his fingers tracing the soft fuzz lining Deku's thighs.

"You're a needy little guy, aren't you?" he teased. Cupping the chastity cage, he mimed a slow pump. His wonderful, delicious fingers were separated by that plastic barrier, and all Deku could do was whimper and thrust his hips up.

Too soon, Kacchan grew bored. He wasn't like Deku. He had a million things on his mind, endless people business to attend to. The first of which was taking a shower. Rising up, he patted his thigh, motioning Deku to follow him. On all fours, Deku had to scramble hard to keep up with him. He had gotten pretty good maneuvering around, although his mitts still slipped on the linoleum.

Kacchan led him back to his bedroom. The windows here were wide, stretching almost all the way down to the floor. Fortunately, they were on the top level, so there was no risk of anyone peeking in and seeing them. Privacy came at a premium when you were a hero, and if word got out about Kacchan's off-duty entertainment, his reputation might take a hit. That was why when they were in public, Deku had to behave like a normal boy. There were no more clandestine dog walks. That was inconvenient, but Deku didn't bother going out anymore. Everything he wanted was in here.

(Or was it that he wanted more, but knew it was unattainable? Why go out into a cruel world when failure was the only option? He'd never been much as a person. As a puppy, at least he had a place.)

With very little fanfare, Kacchan stripped off his clothing. His hero suit clung to him, tacky with sweat, and the way he had to peel it off made something inside Deku throb. This everyday domesticity still felt like a treat, like something private he shouldn't be allowed to see. At the same time, Kacchan was so comfortable around him, acting like it wasn't a big deal, like he wasn't even there. He had the same lack of self-consciousness as someone changing clothes in front of their pet.

I'm definitely a little fucked in the head that that makes me so horny.

But it did. The more Kacchan treated him like a dog, the more Deku wanted to please him. For the time being, that meant waiting patiently while Kacchan showered. Deku shifted on his haunches, lightly grinding his tailbone into the floor, feeling those pulses shoot through him. Kacchan's cock would feel even better– if he was lucky enough to get it. As much as Kacchan liked getting off, he seemed to like tormenting Izuku even more. There would be stretches of almost a week where his master would abstain from any sex just to watch how desperate his dog got. Deku hoped they weren't in one of those periods now.

At last, the hiss of water snapped off, and Kacchan emerged from the bathroom. He was accompanied by a cloud of steam, misting around him like he was some angel emerging from the clouds. Freshly cleaned like this, his skin shone, practically golden in hue. Everything about him was perfect.

"Hey, no drooling on the carpet," Kacchan said, giving his towel a playful crack in Deku's direction. One other thing Deku adored about him: Kacchan wasn't the least bit shy about nudity. He always emerged from the shower with his towel draped around his neck, and he was never in any hurry to dress. That presented Deku with many opportunities.

Plopping down on his bed, Kacchan looked out the window at the city below them. To Deku, the snarl of buildings had all the beauty of a tangled thicket of thorns, stretching in all directions around their little tower like something out of a fairy tale. Judging from the pride Katsuki had in his job, Izuku was willing to bet that the man felt something slightly different. That was his city, his kingdom. He could sit on his bed and observe it for hours.

But Izuku had been waiting all day for his master to come home, and he wasn't about to be satisfied with standing around watching Kacchan watching. Letting out a little huff, he nudged his face against Kacchan's thigh.

"Always hungry for attention, aren't you?" Kacchan sneered.

There was no real fire to his insult. As Deku had learned over the years, that was just Kacchan's preferred method of communication, derision a mask for fondness. Reaching out with one hand, he ruffled the hair on Izuku's head. That was bliss. It was like finally getting a hit of his drug of choice, right when he was on the cusp of withdrawal. Deku leaned into the touch, his eyes fluttering.

"What else are you hungry for?" Kacchan asked, fingers sweeping down to hold Deku's chin. He tilted that gaze up, forcing their eyes to lock. Even after getting to know him so intimately, that stare could still send a hot shudder through Deku. Perhaps even more so now that he knew what the man was fully capable of. In those eyes was the feral hunger of a predator.

Kacchan's thumb dragged across Deku's lips, playing with the divot between them. In response, Deku opened his mouth, inviting them further in.

"Let's put that mouth of yours to work," Kacchan said. He spread his knees wide, opening up his thighs like the curtains pulling apart on debut night, welcoming Deku to the show.

By now, Deku was very well acquainted with Kacchan's cock. That thing had been inside his mouth, his ass, ground into nearly every part of his body. He knew the smell of it, the taste, the weight on his tongue. Rather than make things dull, it gave Deku a sense of comfort. Everyone– pet or person– had calming rituals, a routine or happy place they retreated to in order to center themselves. This was Deku's. When his lips connected with Kacchan's cock, he felt peace.

Kacchan was big enough that Deku had to crane his jaw wide, stretching it so that after a few minutes it complained at the strain. It wasn't a bad sensation. So much of Deku's current life was spent in comfort. Once in a while, it was welcome to feel something sharp.

Grabbing him by the collar, Kacchan pulled Deku down onto his dick. The collar was another one of his expensive indulgences, premium leather, soft yet unyielding against Deku's skin. It was loose enough to not bother him during the day, but the second Kacchan slipped a couple of fingers underneath it, it was just enough to remind Deku that he shouldn't take any breath for granted.

"It's been a while since I let your dick out," Kacchan mused, rocking gently into that mouth. "What do you think, have you been good enough to earn a treat?"

In response, Deku shook his hips, sending his tail wagging back and forth. Honestly, at this point he didn't care. He'd been without his dick long enough that it didn't preoccupy his thoughts in the same way it had when he was a younger pup. Orgasms? Nice. But those didn't need to involve his dick.

Kacchan hit the back of his throat, and the resulting wretch made Deku clench all the harder around the plug in his ass. It was equal parts pain and pleasure, one end of his body pushing away while the other sought deeper.

Above him, Kacchan's eyes closed in bliss, his lips parting as he let out a deep sigh. This man could have had anyone he wanted. He was a celebrity, adored by his fans, any one of which would have jumped at the chance to be where Deku was right now. Yet against the odds, it was Deku kneeling there– worthless, quirkless Deku– with Kacchan's dick buried in his mouth.

Tugging on the collar, Kacchan pulled him off his dick. Deku whined and strained against his hold, still hungry for more, but all this did was elicit a chuckle from the man.

"We've got bigger plans than that. Roll over, boy."

As always, Deku was quick to obey his master's command. No longer was he the disobedient, incorrigible mutt from his teenage years. Now, if Kacchan asked something of him, he was eager to comply. He'd learned that the faster he did, the quicker he got his satisfaction.

With his legs spread and his arms curled up and tucked on his chest, Deku waited for the next step. His breathing was harsh, and his body trembled with want and need. He felt the slow push of Kacchan prodding his tail plug, and braced himself for the sharp yank of it leaving. That didn't come. Instead, he felt the pressure increase as Kacchan's fingers sunk deeper, one trying to worm in next to the existing plug.

By this point, Deku had experienced a lot of things in his ass. The space was occupied more often than not. So this stretch wasn't impossible for him, but it was unexpected. He whimpered, peeling his head off the floor so he could look to see what his master was doing. When he met the man's gaze, his smirk was feral.

"It's always a drag to have to fuck a puppy without a tail," he said, forcing one finger deeper in. "What say we just keep your plug in this time?"

A choked sound left Deku's throat. He'd been so good, hadn't talked for almost a week, but he almost broke right then. It wasn't that he didn't want it, just that he didn't think it was possible. But the idea of Kacchan fucking him with his tail in… it had crossed his mind before. It was constantly frustrating that he only had one hole, that he had to choose between the satisfying sensation of a tail brushing against his ass or his master's hard, hot cock. Both sensations were part of who he was, the things that completed him.

So instead of refusing, of voicing his doubt, he chose to instead spread his legs as wide as he could and trust Kacchan to make the decision for him. If it hurt, well… a lot of sex stuff hurt at first. It had hurt the first time Kacchan had shoved something up his ass, the first time he'd been forced to orgasm without touching his cock, those first few months in his cage. If Deku had learned anything from his time as a pup, it was that he could get used to anything if he just grit his teeth and beared it.

Kacchan's fingers worked around the plug, slowly stretching him out, pushing against his prostate in the process. Inside its cage, Deku's cock leaked and pulsed, flashes of heat going through it as it tried to get hard and failed. He was in a small enough cage now that he couldn't even get hard. Instead, that heat was redirected elsewhere, his entire body growing hot, feeling like he was about to combust.

"That's right, you're gonna be a good boy for me," Kacchan instructed. He had two fingers in, one on either side of the plug, and the stretch was such that it felt like Deku's lungs were being dragged down to the pit of his stomach. Everything was coiled tight and burning, and he held perfectly still, afraid if he moved something would break.

Then the fingers were gone, but the plug remained. Deku felt himself flutter around it, his asshole constricting as if realizing what it had lost and lamenting. It didn't have long to be lonely. Something else was there, pressing against his entrance.

Deku moaned. Technically, that wasn't a dog sound, but Kacchan was usually lenient with him when they were fucking, so long as he didn't say words. So long as he was good and patient and took what he was given without complaint.

Just like he had anticipated, it hurt. There was the sting, but it wasn't just that the skin was being stretched wide. There was also the feeling of that hard plug being pressed against his insides, the edges normally too smooth to notice, now like being pressed into a granite countertop. Then there was the feel of Kacchan's cock. It was unrelenting, stretching him open around the plug, surging deeper inside him. The only thing Izuku could do was cry out, spine contorting. With his hands locked away inside the paw-shaped mitts, he couldn't even grab onto anything for support. He was completely at Kacchan's mercy.

"That's right," Kacchan breathed, finally sliding inside him. "I know you like this, you bitch."

Deku wasn't the only one being pushed to the limit. That space must have been so confined, and the plug pushed into both of them, refusing to budge an inch.

"Mmm," Deku groaned, bucking. In order to not scream out the name of his lover, or even plead to some deity, he bit down on his lips until they were bloodless white. Kacchan wasn't even thrusting. He didn't need to. The pressure was constant, unrelenting, and looking down the white streak of his stomach, Deku saw the glint of the cage twitching. His poor dick wanted out, ramming against its enclosure like an enraged beast searching for escape.

Escape was not an option.

Slowly, with gritted teeth and a hiss, Kacchan withdrew partially only to slam back in. It was a struggle, his dick dragging against the lip of the plug, and it certainly couldn't have been comfortable. But between them, sex had never been about comfort. It was always intensity, of pushing and grappling and going as hard and as fast and not letting up until everything was blurred white. That's where they were racing now, and Deku's vision danced with spots. He whined and groaned, and even if he had been allowed speech, he wouldn't have been able to find the words. All he wanted was to meet the end, to feel Kacchan release inside him.

In terms of sex, Deku only ever thought about Kacchan's orgasm. That was the point. His own was fickle or elusive or altogether not important. The point of sex was to show his master he was useful, to be able to endure even something as intense as this until the very last moment.

When Kacchan came, it was with an animalistic growl of his own, hunching over Deku and grabbing his hips hard enough to bruise. Deku felt the warm sensation, felt it shoot deep inside him, rushing to find a square inch of space in his crowded asshole. There was less than usual, so as a result it sought deeper, soaking him in spaces they'd never reached. Deku shuddered with it, as always delighted to reach a new frontier. Just when he'd thought they'd capped out, explored every available horizon, Kacchan extended the borders of the map.

There wasn't much basking in the afterglow. Kacchan was quick to pull out, not risking overstimulation in that small space, and he hissed as he finally popped free. The tail plug remained, but after the festivities, it felt small and insignificant. Deku had been overstretched to the point that he felt himself leaking around it, the jizz finding space to seep. Messy. He'd have to clean it up later.

With very little fanfare or hesitation, Kacchan picked himself up and proceeded to get dressed. He'd never been one for post-coital cuddles or aftercare, and was rarely phased by anything– even a mind-blowing orgasm. That was just one of the things that made him so amazing. On the other hand, Deku remained on the ground, breathing hard and piecing himself back together. It was times like this that being a puppy felt most natural. He didn't have to pretend to be some wordless, brainless animal. He was fucked stupid and content, floating in the liminal space between coherent thoughts.

It didn't last. After a while, he came back to himself, and then he was rolling to all fours and pushing himself up. Meanwhile, Kacchan was fully dressed, and he beckoned Deku to follow him. Kacchan settled into the couch, Deku sitting on the rug at his feet.

"All right, I'm going to let you go human-mode for a bit, because I have something important to discuss with you."

Immediately, Deku felt a sour pit in his stomach. At times, being stuck as a puppy could get frustrating. There were some things he missed. He missed browsing forums on the internet, or building model kits, or eating things off the table with a fork and knife. But conversing with Kacchan… wasn't on that list. It had always been difficult, fraught with conflict and miscommunication. As a dog, there was no longer that tension. All he had to do was be cute and wag his tail, two things which he personally thought he excelled at.

So he didn't talk right away, although he did shift to kneeling, paw mitts resting awkwardly on his knees.

"So I found a guy–" Kacchan started, and Deku's stomach roiled with nerves.

Oh my god he's replacing me. I always knew it would happen, I just didn't expect it to be this soon.

"–who can give people quirks."

He stopped there, waiting for Deku's reaction. It took a moment. Deku's brain had to halt its current panic, reverse, comprehend, then throttle full speed into excitement.

"What? What? A quirk? Like a real quirk? For me?"

Instinctively, Deku shifted back and forth, shaking his hips, wagging his tail. He couldn't help it. This was exciting.

A quirk.

It has to be some sort of joke, right?

"B-but what would I even do with a quirk?" Izuku wondered out loud.

"Oh, you'll find a use," Katsuki said with a wink.

"Are you… really gonna help me get a quirk?"

There it was. Now that his human brain was online, he was filled with doubt and suspicion. People were never kind to Izuku, the quirkless nobody.

But if I got a quirk, I wouldn't need to be a nobody anymore. Maybe… maybe I could be somebody. A real person.

"I might," Katsuki drawled, recrossing his legs and leaning back on the couch. "It depends. Are you gonna be really, really good for me?"

"Of course!" Izuku replied instantly. "You know I'm always good for you, Kacchan."

The hero reached out and ruffled his hair, jostling him hard enough that his floppy pup ears flapped with the force of it.

"Yeah, you are. Well, show me how much you want it tonight, and tomorrow let's pay this dude a visit."

Ecstatic, Deku squirmed onto his lap, eager to give Kacchan whatever he wanted.

A quirk. Like a real person. Would he still be Kacchan's little puppy after that?

Could he be something better?

He'd just have to wait and find out. Being in human mode was honestly uncomfortable these days. Izuku was so used to walking around on all fours, to the soft squish of his mitts against the floor. Somehow things seemed cozier when he was only a couple of feet off the ground. In contrast, everything seemed so far away, striding behind Kacchan on two legs.

They'd come to a bar, which wasn't the sort of place Izuku would have expected to find a man who could dispense quirks. Somehow, he had imagined him living in a mansion. Or at the very least, a doctor's clinic. But instead, they were in a place filled with cigarette smoke, the clack of the pool table in the back occasionally ringing out like gunshots. Everyone carried the subdued tones of poverty, the shirts faded and in need of replacing, the pallid skin of those with no dreams and nowhere to be. The looks they shot the couple were not welcoming.

"So, um, how did you meet this guy?" Deku asked, skittering closer to hide in Kacchan's shadow.

"Oh, I found him on the job while investigating a crime ring. He's absolutely breaking the law," Kacchan replied casually. "I should turn him in, but he's not really hurting anyone, so I agreed to look the other way in return for him doing this favor for us."

"Kacchan!"

It wasn't out of character for Kacchan to be reckless. When the man wanted something, he got it, regardless of the cost. To himself– or other people.

"Look, it's not that big a deal," Kacchan replied. "People use their quirks off the book all the time. He ain't hurting anyone."

However, knowing that this meeting was perhaps slightly illegal put a jitter in Izuku's step. He stuck close to his master, feeling acutely naked without a collar or tail. Fortunately, he still had the chastity cage on– that went with him everywhere. The slight tap of it against his thighs as he walked helped ground him. If something went bad, Kacchan would be there to protect him. After all, he belonged to Kacchan, and Kacchan always took care of what was his.

Kacchan led him through the bar, to a back room that was guarded by a stern mutant type, protruding ram horns curling in a tight spiral parallel to their jawline, giving them the look of someone who did not like to be messed with.

"You got business here?" he asked, voice immediately irritated. Obviously customer service was not his usual line of work.

"The doctor is expecting me," Kacchan replied coolly. "Tell him Bakugou is here."

Ram-man ducked into the room, conferring for only a moment before stepping out and swinging the door wide, granting them entrance.

As much as the location didn't match Deku's expectations, the doctor was even more unusual. He was a thin man wearing a too-large coat, the sleeves hanging down over his hands. Whatever color his eyes were, Deku would never know, as he wore aviators that likewise looked too large for his face. His hair was slicked back, his demeanor serious and a bit cautious.

"So after these we're even, yeah?" he asked before the couple had even sat down at the table. "I throw you a bone, you let me off the hook, right?"

"We'll see," Kacchan replied, sinking down into his seat and kicking one foot up onto the table between them. "Deku, this is Dr. Moreau. Moreau, Deku."

"Um, pleased to meet you," Deku replied, inclining his head. He wasn't sure what to say to this man that might be able to fulfill his wildest dreams, who looked like he had just remembered his parking meter had expired and wanted to bolt. Everything about him was slightly jittery.

"All right, doc," Kacchan said, cutting off any other attempts from Deku at smalltalk, "go ahead and tell the boy here what you can do."

The doc turned to Izuku, the end of one sleeve flapping slightly as he nervously tapped his hand on the table.

"I've got a mutation quirk, see? Nothing drastic, I'm not gonna make a Gang Orca outta ya or anything, but I can grant certain features."

"Wait, do you mean you have a mutation quirk," Deku asked, eyeing the fairly normal man up and down, "or that you… can mutate others?"

"Both, see?" The man replied, rolling up the sleeves on his jacket. "Anything these paws touch gets transmogrified, ya dig?"

When he said paws, he was being literal. Hidden underneath the jacket were fuzzy, clawed, honest to god paws. It was like the mitts Izuku wore around the house, except as he watched, the doc flexed them, twiddling the blunt fingertips.

"Not gonna lie, these right here make my life pretty fucked," he said, clenching the paws into fists. "Fella can't even pick his own nose with these mitts. Have trouble dressing myself, eating, taking a piss. But heaven forbid I reach out and touch someone else."

"What happens when you do?" Izuku asked.

"They get furry-fied," the man replied, giving him a 'duh' look. "Isn't that why you two are here?"

"F-furryfied?" Izuku squeaked.

Maybe he didn't use it as much these days, but Izuku had grown up using the internet. He knew what furry meant. The demand for people with certain mutation quirks was high. The porn was intense. The subculture was… a world unto itself.

"And it's… permanent?"

Shrugging, the doc replied "More or less. Depends on how hard I'm concentrating when I give ya the ol' fuzzy handshake."

"Woah woah woah," Izuku replied, standing up abruptly from the table, "I never agreed to… to a fuzzy handshake."

"Sit, Deku," Kacchan said.

"No," Izuku snapped. "Kacchan, you said you were gonna get me a quirk. "

At his sides, his hands balled into fists, fingernails pricking into palms. It had been a while since his hands had been out of the gloves and he'd even been able to feel his fingernails; they were long and sharp from lack of maintenance. He wasn't about to go and… get rid of them permanently.

"This is a quirk," Kacchan growled back. "What were you expecting? Someone to dispense super strength of the ability to leap over tall buildings? Passing powers out like candy? A mutation quirk is still a quirk."

"Kacchan, this is my body, " Izuku reasoned.

At this, Kacchan huffed as if he had just told a joke. Truthfully, the words felt false coming out of Izuku's mouth. He knew that he had long ago surrendered solitary autonomy of his own body in exchange for small, intermittent slices with Kacchan's. He was the clear winner in that transaction, his own worthless husk of a mortal coil in exchange for being near someone almost divine in body and potential. However, as deplorable as this body was, it was his. He didn't want to cast it aside entirely.

Sensing his distress, Kacchan rose from his seat. Reaching out, he took Izuku's face in his hands. As always, they were warm and soft like butter just about to melt, every bump burned away by his quirk. Holding that face, Kacchan made it so their gazes locked, so that Izuku couldn't look anywhere else but him. His eyes were red and riveting, hypnotic in their intensity, and Izuku found himself unable to look away.

Gently, firmly, Kacchan said, "Don't you want everyone to think you're a cute puppy, Deku? Don't you want to be able to walk down the street with your tail out, wagging it happily for the world see?"

At his words, something hot and prickly filled Izuku's chest. He and Kacchan had flirted with exhibition and being in public before. The couple of events at UA came to mind, as did the nightly walks during their first year together. But now that Kacchan was in the spotlight, they couldn't take stupid risks anymore. Deku had to be his dirty secret.

But a mutation quirk… well, it would be like hiding in plain sight. He'd be allowed to be a pup out and about, and anyone who objected to it would look like a bigotted monster. Granted, some people still would, as mutants faced discrimination, but…

Izuku gulped. It felt like something large and hot was lodged in his throat.

"If I do this," he said, voice low, "there's no going back."

Katsuki smirked. He had a beautiful smile, and it was a shame he showed it off so rarely. An even bigger shame that the times he did show it off was usually when he was feeling especially predatory or smug, like now.

"Silly Deku," Kacchan whispered, one hand sneaking up to ruffle Deku's hair. "We crossed the point of no return a long time ago."

For a moment, they hung suspended, eyes locked on each other. Then a sharp cough broke the silence.

"So uh… do you two need some privacy?"

Doc shifted uncomfortably in his chair. This broke the magic, popped the bubble the two men had been suspended in, and Deku pulled away. However, it was less out of shame and more out of a need to get down to business.

"Exactly what will your touch do?" he asked. "What parts will it change? Do you have photos of your past work? Can I meet any of them? Is it painful?"

By his side, Katsuki let out a grunt, something bordering on fondness, and sank back down into his seat.

"Here we go," he drawled. "He's gone full nerd mode."

Fortunately, the man was willing to explain his quirk, although he didn't have much in the way of references. Apparently people didn't usually ask for them.

"I get requests all the time," he replied. "Plenty a people are looking for a change, a chance to walk on the wild side, you dig? They want fangs or a tail or wings. I can give 'em the specifics. A full custom job."

So that was it, then. With this man's quirk, he could become Kacchan's little puppy– for real. The entire world would be able to see him trotting along behind his master. A boy and his dog.

It wasn't quite the same as being boyfriends, partners, but maybe to an outsider… maybe if Kacchan started taking him places publicly, maybe there wouldn't be much of a difference. Still, it was a very big commitment to make.

"I need to think about it."

Without even looking, he could sense the irritation and disappointment radiating off Kacchan. The man had fully expected him to just go along with it, to do whatever he suggested. Normally that was how these things went– and Izuku was fine with that. Kacchan's decisions tended to be for the best, anyways. But for this, Izuku wanted to make up his own mind. He wanted to be sure.

Shrugging, Doc said, "Hey, no skin off my back. You change your mind, you know where to find me."

Izuku did not put the puppy gear back on when he got home. He needed time to think, which for him traditionally meant pacing and nervously fidgeting. When he was in pup mode, he did very little thinking at all, which was a blessing, but for something like this, he needed space in his mind to turn it over. So no gear, and no special time with Kacchan. The man left for work, leaving Izuku all alone in that magnificent penthouse apartment.

He couldn't stand it. It didn't matter if the place cost a fortune, if it was spacious and luxurious. Suddenly the empty space was a reminder of how much of his life was spent just waiting for Kacchan to return. How empty it was without that. How much he needed him.

To take his mind off things, he went for a walk. It had been a while since he had been out and about unaccompanied, and it felt hollow. Perhaps it was because he was self-conscious, but he felt like even without his gear on, people could tell he was somehow a freak. It was like Kacchan had warped the texture of his soul, and now he couldn't fit in with everyone else.

If he couldn't fit in, what did he stand to gain by refusing Kacchan? It wasn't like he could go back to life before him. No, he was older now, had spent the last years of his youth wrapped around this man's finger. That couldn't be regained. On the other hand, there was so much to lose.

It's not like it would be the worst thing. There are plenty of mutant types in the world, so I wouldn't be alone.

As he walked, his eyes scanned the crowds of people passing him. Every now and then, there would be someone that stuck out like a sore thumb, whether it was because of a feathered crest rising from their head, a scaled tail sweeping behind them, or some other protrusion from their bodies. His eyes landed on one man, skin thick and trenched like the bark of an ancient tree, walking hand in hand with a petite, cute blonde girl. It was such an odd couple, one completely normal and the other barely passing as human, that Izuku couldn't help but stare.

If he and Kacchan ever took their relationship public, it would look that way to strangers. Maybe Izuku wouldn't be the oddest person in the world, but everyone would look at them and think 'Why would he date such a loser?'

People would think that now anyways, if they knew we were a couple.

"Hey," the man growled, noticing Izuku's gaze, "didn't anyone ever tell you it's not polite to stare?"

With a squeak, Izuku tore his eyes away and slunk back into the crowd. He felt himself burn hot with shame. Of course an average person didn't want to be gawked at, didn't want his eyes all over them.

But the same could happen to me. People would see me passing in the street, and they wouldn't be able to stop and stare.

Kacchan's vision for him was as an adorable dog that everyone cooed over, but one that only Kacchan could have. There was something in that man that needed not only perfection, but the envy of others to survive. Part of their relationship had always been about that public claiming.

(The alley, the other boys, the grinding him into the dirt so others could see how far above Deku he was.)

Did Izuku want to be claimed? Or did he just want to please Kacchan?

His feet hurt from walking, his mind hurt from spinning in circles. With nothing else to occupy his time and no hope of coming to a conclusion, he turned and headed home.

Home was empty. Kacchan still wasn't back yet, which meant he had nothing to do. Even though he was out of pup gear, Izuku found himself waiting by the door, foot bouncing nervously.

This was what his life had become. Without Kacchan in it, it was completely empty.

The door finally creaked open, and Izuku jumped to his feet, ecstatic. Greeting Kacchan as a human was weird, because the man wasn't openly affectionate with him. He gave Izuku a slight nod, closing the door behind him and considering.

"So?" he said, looking him up and down. "Been busy?"

"No," Izuku replied. No point in lying– they both knew that was the truth. "But I have been thinking. I… I'll do it."

At this, Kacchan's eyebrows lifted up. Izuku had a hard time believing that the man was surprised that Izuku had finally given in– Kacchan knew his pet too well– but perhaps he was surprised at how little effort it had taken. After making such a fuss, all it took was one empty afternoon in his own mind, and Izuku was eager for an escape.

"We can have you pupped tomorrow if you're serious," Kacchan said.

"I am serious, but… I want to do it slowly," Izuku explained. "That's my condition. It has to be in increments, and I… I'll stop it if I don't like it. Okay?"

Kacchan nodded once. The smug expression didn't leave his face.

"All right. I'll make the call."This might tingle a little, kid."

Deku gripped the chair beneath him, knuckles drained white with the intensity. He had never been good about getting shots, or going to the dentist, or enduring even a mild amount of pain. It wasn't that he didn't know what pain felt like, merely that he would tense up so much that it inevitably made things far worse.

Moreau's paws were cold, and not at all soft like a kitten's. Instead, it felt like they were part cactus, scratchy where they pressed into Izuku's waiting hand. Too nervous to do anything else, Izuku squeezed his eyes shut and tried counting to ten.

One, two, three.

His body flushed hot. It was like the sharp sting of shame, like the sudden blush of public humiliation. He had felt that often enough in his life to recognize it.

Four, five, six.

True to Doc's claims, he did tingle a little in his extremities. His ears, his nose, his fingers, his toes. All buzzed softly, a squirmish sensation.

Seven, eight, nine.

It itched. Izuku wrinkled his nose, resisting the urge to claw at himself, at his skin. Underneath it all was the current of paranoia, the fear that when he opened his eyes, he wouldn't recognize himself.

Ten.

Doc released his hand, and Izuku tentatively pried his eyelids open. Nothing had changed.

"Did it work?" he asked, turning his hands over and inspecting them. They were still the same ten fingers, the same soft palms.

"What, you think it happens with a snap of the fingers?" Doc drawled, shaking his sleeves out so they once again covered his paws. "Yer outta yer gourd, kid. This stuff takes time. Your body's gotta osmositize some brand new cells and all that. Science stuff."

That had not been in the explanation, and somehow, the prospect made Izuku even more nervous. Now he'd have to go home and wait for the changes to come, not knowing when they'd show up. But whining wouldn't change anything, so Izuku just thanked the Doc and followed Kacchan out the door.

"So how long until you're ready for the next step?" Kacchan asked. He had been less than pleased with Izuku's demands to take it slow, and thought the boy was being silly.

"I don't even know what the changes are yet! I have to see how this round feels."

Kacchan rolled his eyes and huffed, but for now, he didn't press the issue.

The next morning, Deku was woken by the sound of Kacchan's feet hitting the floor. It wasn't that the man stomped around early in the morning– Deku merely heard the soft pad of ankle against hardwood, and suddenly he was wide awake. He watched from his pillow in the corner as Kacchan got up and went to the bathroom. Even with the door closed, Izuku could hear everything going on: the cascade of early morning piss hitting the bowl, the squeak of the faucet turning, the distant rush of pipes sending water through the walls.

Okay, that is definitely new.

So too were the smells. Mostly it was the stale cloud of dust lingering around the apartment, even though Kacchan was a very good housekeeper. And it wasn't just that Deku could identify scents– somehow he could also get a sense of the quantity. The pile of dust behind the bookcase was stronger than the one on the windowsill, for example.

Okay, enhanced senses. That's actually… really cool.

It felt like a real quirk, like something beyond the limits of an ordinary human. Having been trapped as an ordinary human most of his life, Deku was one to know.

Curious to find out what else was happening, he got up from his pillow and inspected himself thoroughly. He was back in his pup gear, which meant it was a bit difficult to get all the nooks and crannies. The mitts prevented him from just feeling along, so he had to contort his body to see every angle.

Nothing. He was still completely average. He just smelled and heard slightly better.

He'd just have to be patient. Since he was a dog, it wasn't like he had much else to do. He was in no rush.

"Does puppy likes his tail played with?" Kacchan crooned, again giving Deku's tail a light tug.

In his lap, Deku whimpered and writhed. His cock felt so heavy, sitting hot and hard in its cage, and he pressed up against it as best as he could. Again another tug, the wide brim of the toy bumping up against his outer ring of muscle, making him shudder. If Kacchan was feeling especially cruel, he'd hold the toy so that the widest part was lodged right in the opening, forcing Deku ajar and making him whine with the sting of it.

Kacchan wasn't feeling cruel. Instead of tormenting Deku, he yanked the tail out, leaving him feeling empty. But that meant that his fingers would be in there soon, and Deku shuddered and tilted his ass up higher.

"Hmm? What's this?"

Reaching out, Kacchan's thumb stroked against something right at the border of ass and back, just above where his crack ended. The result was a tingle lancing through Deku's spine, the same almost-ache of a sore muscle being stretched. Craning his neck, Deku did his best to turn around and look. He couldn't see. It was in his blind spot, but he felt it. There was a tiny bump there, just a soft protrusion.

"Would you look at that?" Kacchan breathed. "That looks like the start of a tail."

Now Deku was twisting even more, trying desperately to see what Kacchan was referring to. If there was a tail on his butt, he wanted to see it!

Unfortunately, his spine was not cooperating, and the most he could see were his legs extending past Kacchan's lap.

With the meat of his thumb, Kacchan rubbed around the small nub. Deku closed his eyes, soaking in the feel, mapping it out in his brain. Right now it seemed so small, insignificant. But if he concentrated, he swore he could feel the way it extended, the little bit of his spine poking out beyond the borders. There were new vertebrae there, a growth both unnatural and incomprehensible.

"All right, enough about you," Kacchan said, unceremoniously shifting Deku out of his lap. "Now it's my turn for attention."

As disappointed as Deku was to not spend more time exploring this radically new development, Deku also could never say no to a chance to get Kacchan off. His body would be there later, when he was alone or bored. Kacchan was here now, his flush dick hanging heavy and wanting between his legs. Deku knew what was expected of him. Opening his mouth wide, he let that cock slip past his lips, heavy on his tongue, filling every part.

He'd gotten very good at breathing through his nose, taking rapid gulps of air in the space between thrusts. He'd learned how to relax, how to calm the panic of his gag reflex. There was that blissful mindspace of knowing he was being used and useful, that he was contributing instead of just being dead weight. It was the closest he ever came to power.

Something strange happened to him in the middle of the blowjob. Like usual, he was floating in the happy headspace of knowing everything was right. The exuberance shook through him… and kept shaking. He felt a distinct vibration travel down his spine to the very tip.

"Would ya look at that?" Kacchan said with a chuckle. "Your little nub is twitching. Looks like it's trying to wag."

Deku let out a curious sound, part moan and part squeak of surprise. So often he'd worn his tail plug during these kinds of things and shook his hips to get it to wave back and forth. He loved the way his tail curled over his back, brushing against him as he wagged it. And also, there was no point in denying that he really, really liked the way it got him off. It was his prostate's snuggly friend, and without it, he'd go around feeling empty most of the time. Replacing it with some sort of quirk concoction tail meant he would lose that.

But being able to wag a tail for real… it wasn't like he'd never have something in his butt again. They could find other things to stuff him with. But having a real tail and being able to show his happiness, not even being able to contain it…

When they were finally done with the blowjob, Deku held up his paw and whined, his signal for wanting to speak. When Kacchan nodded his head, Deku blurted out, "I think I'm ready for the next session."

The next time he saw Doc, he could feel his little nub of a tail twitching inside his pants. Between that and the ever-present chastity cage, there was a lot of action going on downstairs. Still, he did his best to concentrate. He wanted to note every minor change.

"We're still taking it slow," Izuku explained, "but… if you could prioritize the tail? I… don't think I'd mind that being bigger."

"Yer gonna have to start cutting holes in yer pants, kid," Doc said with a shake of his head. Still, he rolled up his sleeves and went to work, taking Deku's hands in his own paw-like ones.

Once more, Deku felt the flood of sensation, the tingling followed by that flash of heat. Even concentrating hard, though, he couldn't notice any immediate changes. Like Moreau had told him at their first meeting, it would take time. Patience was excruciating.

Still, he went home, he went back to puppy mode, and at least now he had things to look forward to– some demarcation of the days. It was amazing the transformation that was happening, both emotionally and physically. While Deku never would have described himself as depressed (he lived with Kacchan ), his life had taken on the pallor of routine. Now, every day he had something to look forward to.

His master spent even more time than usual running hands up and down his puppy's body. He'd play with Izuku's twig of a tail, now a couple of inches long and showing a hint of fur. It could be a bit tricky to get ahold of, as Izuku would wag it furiously upon even the slightest hint of attention. Even when Kacchan had it firmly in his grasp, Izuku could feel the vibrations of his body doing its best to wag and wiggle.

When Kacchan wasn't tugging on his tail and making fun of its tiny size, he was rolling the tips of Deku's ears between his fingers. Those, too, had sprouted a fine layer of peach fuzz. When he looked in the mirror, he could see the tips poking up above his dense curls. The shape was changing, becoming more triangular. These, too, were prone to twitching, albeit in curiosity. There were so many exciting sounds! Things Izuku had never even stopped to consider, like the hum of the fridge or the buzz of the lights.

Also, Kacchan's voice was even sexier the better his hearing got. Such a sultry purr, enough to make his stomach do a flip flop in excitement.

"Do you wanna do some tricks for me?" Kacchan asked, the gravel-grit of his voice flooding Izuku with warmth. "Let's see if you can be a special boy."

Yes. Yes, I can be a special boy!

Kacchan got out his bag of treats. It was just a collection of cheap corner store snacks, but since Deku rarely left the house by himself, they might as well have been exotic wares from a far off land. Shaking the bag so that the contents rattled around, Kacchan drew his attention. They'd started this evening ritual a couple weeks ago, after the transformation started to be noticeable.

"Can you sit?" Kacchan asked, taking out a treat from the bag. A single gummy bear, translucent in the living room light.

Immediately, Deku's ass snapped to the floor. Sitting was easy. He knew how to sit. So easy. Still, it was hard not to move around, to dance in joy at the attention and the treats, and he shifted where he squatted, pushing his weight from one foot to the other and whining.

"Good boy," Kacchan said, proffering the treat on a flat palm. Deku gulped it up, not missing the chance to lave his tongue over Kacchan's wonderful skin.

"Roll over."

Deku did as asked, throwing himself to the ground in a fervor. He showed his stomach eagerly. His stub of a tail patted softly against the hardwood, showing off just how much he wanted it.

It wasn't like they'd never played around with commands and giving treats before. And it wasn't like Izuku hadn't thoroughly, rabidly enjoyed it all those times before. But there was something more now. It was like now when Kacchan called him good, he believed it. He believed that he was a good boy, that he not only could earn love but deserved it, and that didn't make him selfish or sick.

Was that part of the transformation? Was his brain becoming more dog-like? Or was it merely another layer of the kink they were uncovering?

Impossible to say, so Deku didn't waste time worrying about it.

Kacchan placed another treat in his mouth, and Deku swallowed it down eagerly. Since the pup was still on his back, his master reached out and began stroking along his front, admiring Deku's body. There was a bit more hair there than usual, but it wasn't coarse like his typical body hair. It was ever-so-slightly fuzzy, a mild down that must have felt like suede to the touch, judging from Kacchan's lidded gaze.

"You really are a good boy, aren't you?" he breathed. "My perfect little guy."

He reached up, cupping one of Deku's pecs in each hand, gave them a light squeeze. Deku made himself as open as possible, spreading his legs and arms, lying there as motionless as he could. It wasn't very motionless. He couldn't help but squirm. It was like his body didn't even care where it was going, just that it had so much energy that he had to get it out. Everything about life was exciting and wonderful.

"I wanna do something extra fun today," Kacchan said, and Deku wriggled on the floor, his tail thrashing.

From his pocket, Kacchan extracted the key to Deku's chastity cage, deftly removing the device. As always, the temperature difference was like a slap, that thin plastic sheathe somehow more insulating than a thick blanket when he was used to it. Deku whined at the discomfort.

"It's okay, boy. Stay here. Stay."

That was the worst command of all. Deku whined, thighs shaking as his body adjusted to having his dick out. It was immediately getting hard, anticipating what was to come.

Kacchan was gone only a short moment, coming back from the kitchen with a butter knife and a jar of peanut butter. The smile on his face was feral and ten kinds of mischievous.

"I heard about this game on the internet," he explained, twisting off the lid. "Apparently some sickos like to play this with their dog. Sit up."

Curious and only slightly apprehensive, Deku did as instructed. He watched raptly as Kacchan scooped out a generous dollop of peanut butter. With his enhanced smell, Deku felt like he was face deep in it, and he unconsciously started salivating.

"Hold still."

Kacchan reached out with the knife, dipping past Deku's face. Deku's resolve held firm, and he didn't flinch. Instead, he watched in fascination as Kacchan spread the peanut butter over his uncaged cock. The sensation was viscous and surprisingly warm, coating him in a soft blanket. He couldn't help but hiss, his body jubilant and his cock celebrating.

When Kacchan had spread it all over, he leaned in close and whispered, "Now lick it off."

Deku looked at him for a moment, unsure. They had experimented with auto-fellatio once before, but Deku had proved not flexible enough. And Deku was normally quite limber, so it had seemed outside the realm of possibility. However, the peanut butter called to him, and the part of his brain that chased raw sensation didn't want to waste time agonizing about whether or not it was possible. It wanted to strain forward and try. So he listened to it, bending himself in half and stretching as far forward as he could. His cock was hard and aching now that he was free of his cage, so at least he had it that much closer to his face.

To his surprise, when he extended his tongue, it actually reached. Just barely, just the tip, but it was exciting to even be able to get that far. Exciting– and stimulating. His mouth exploded with the creamy tang of peanut butter just as his dick throbbed with the stimulation.

Encouraged by his success, he shifted, lifting one leg up so he could get a better angle. His tongue darted out, trailing up his member. The pink appendage seemed longer than before, more flexible, enveloping his dick.

From this angle, with his head buried between his legs, he couldn't see Kacchan's reactions. However, he could hear his master inhale at the sight of him sucking himself off. It felt good to be able to put on a show.

Opening his mouth, Deku was able to put just the tip of his cock inside. The taste was salt and sweet, a mixture of flavors that satisfied some deep part of him. He groaned, pushing himself deeper. His spine was bent practically in half, strained, but he couldn't bring himself to care. This felt fantastic, and he wasn't about to stop. His tongue darted out from his mouth, whisking all around his cock, sweeping over the head only to trace the prominent vein down the underside.

"That's right," he heard Kacchan breathe, voice reverent, "get yourself off, you dirty dog."

Deku was trying . All his experience at giving blow jobs was paying off now, and even if he could only get the tip into his mouth, between his extended tongue and his skill (and the fact that his poor, neglected cock barely ever got any stimulation at all) he was having a grand time. If this kept up, he was likely to come, but he hadn't been given permission.

Pulling his head up, Deku looked at Kacchan and gave a whine. The man knew what he wanted. It was the same thing he always wanted– satisfaction. Normally this was the part where Kacchan denied him, delighting in the discomfort that brought him. However, he must have felt benevolent at the moment. Either that, or very curious.

"Go for it," Kacchan said with a nod. "I want to see if you can, just from your own filthy mouth."

Leaning back over, Deku gulped himself down. He popped himself into his mouth, lips loose around the head of his cock, tongue sloppy and eager. Everything felt like bliss. For once, he was in control of his own pleasure, and it was both scary and exciting.

He came quickly. He always did when he was actually given stimulation, and each time he felt a bit of shame over it. However, that shame never overpowered how intense the sensation was, howling inside of him like the most triumphant wolf underneath a full moon.

The inside of his mouth was salty and thoroughly coated, a sticky mess that clung to his tongue. And he couldn't help but notice that his tail was wagging. They visited Doc every couple of weeks. Little by little, Izuku's body changed, slowly being molded into Kacchan's vision for him. It had gotten to the point where there was no hiding it in public. Even if he felt like keeping his tail trapped in his pants (now long and curly, extending midway up his back) and fluffed up his hair to hide his ears, there was no hiding the fact that his nose was a little darker now, his face pushed out ever-so-slightly into a definite snout. So since he couldn't hide that, what point was there in hiding anything else? Izuku walked around with his head held high and his tail waving free behind him, wagging furiously at every interaction.

And he was out in public more. In a strange twist, the more obviously pup-like he became, the more it felt natural to leave the apartment. He was still there whenever Kacchan came home, determined to greet his master, but he also enjoyed long walks, meeting new people, seeing the world. No longer was he worried about the world finding out about his dirty little secret. They had to see him for who he was and accept it.

To the people he met in passing, it was completely normal. They saw someone with a mutation quirk, albeit a cute one, and they would smile and nod and go on with their business. Unfortunately, things got slightly more awkward (and complicated) when it came to meeting people who had known him before the change.

Case in point: lunch with his mother.

Inko now lived alone, retired from her day job, and although she tried to respect Izuku's space and stay out of his life, the sad fact was that he was all she had. He couldn't ignore her entirely. So for the last couple of years, he had played a delicate game of hiding most of his personal life from her. She knew he had decided against college, that he was living with a roommate, and assumed he was working some sort of menial job.

My job is anything but menial.

His job was to be Kacchan's loyal pet, and for a long time he had done that duty in secret. But now here he was, tail protruding from his pants, the whole world seeing what he was really like.

Kacchan told me that once I get far enough along, I can start wearing the collar in public, too.

That would be exhilarating, but it would be one more thing he would have to explain to his mom. Currently, sitting across from her in a cafe and sheepishly wagging his tail, he already felt like he had enough on his plate.

"Sweetie, what happened?" Inko asked. "Was there some sort of quirk accident?"

Oh, thank god I live in a universe where stuff like this just occasionally happens .

"Um, more or less," Izuku replied, rubbing the back of his head. "Yeah, I, uh… I had an encounter with a dude with a mutation quirk."

Behind him, his tail started wagging with renewed vigor.

"How long does it last?" she asked.

The tail stopped. Inko's face was wrinkled with worry, the same look that had dominated most of Izuku's childhood. She was thinking about her poor, damaged baby boy, how life was unfair to him, what she could possibly do to help. To her, this was just one more way her child was being shafted by the universe.

"I actually think… it's permanent," Izuku replied. "And progressive. But it's okay! Really, mom. Oh, mom, please don't cry."

Too late. Inko had started to weep, dabbing at the corners of her eye with a napkin and looking thoroughly miserable.

"Oh, Izuku, we can look for a doctor. There are treatments. I hear UA has a new experimental 'damage reversal' program–"

"Mom."

Reaching across the table, Deku took his mother's hand in his. His fingers were now tipped with dark-colored nails, slightly more pointed than before.

"Please, mom, I'm an adult now. I don't need you trying to protect me, or… or to spend all your money on miracle cures, or agonizing about my life. I'm happy this way. Really."

Inko gave a sharp sniffle, obviously not convinced. It hurt Izuku to see his mother upset, but he wasn't about to stop chasing his own happiness just because she didn't understand it. In time, she'd see that this wasn't a tragedy. Either that, or…

He wouldn't agonize over the 'or.' For now, he tried to steer the conversation to other things, talking with his mom about her life, her health, the latest gossip about their neighbors– the standard safe topics. However, heavy between them was this discomfort, and with it the realization that things wouldn't go back to normal. The more he changed, the more people around him would see him as different. It was a bittersweet thought, but it did nothing to change his resolve.

Izuku knew that dog penis functioned differently than human dick. He'd maybe… looked into it a little bit. Nothing gross! Back before he and Kacchan had even formally begun their pup play, he had wanted to know more about dogs. There had been hours of research, several books checked out from the library, etc. All of that was to say: along with all the other changes he was experiencing, he started to get a sheath, and he knew what sort of things to expect.

It didn't happen overnight. Like all of the changes, it was a bit at a time. One day he woke up and noticed that there was an extra layer of skin around the base of his dick. After another session, it started to turn red. Then, it started to change position.

For a dog, having a penis that naturally rested at a slight angle made sense. It helped them aim where they were marking, instead of having a floppy member they did not have the free hands to aim. However, for a human…

"You're gonna have a hard time wearing pants," Kacchan teased. "It's gonna look like you always have a boner."

"Kacchan, this is serious," Izuku said.

Currently, it wasn't too extreme. His dick was encased in a mild sheath and sat firm at a slight angle, perhaps ten degrees. It was enough that if he wore yoga pants or other tight fitting clothes, then yes, it might look like he was sporting a chubby, but he could still conceal it for the most part. However, while Izuku had never precisely measured dog dicks, he was pretty sure most of them naturally rested at a much steeper angle. In fact, didn't some of them practically point up their stomachs towards their face? If it got that extreme, Kacchan was right. He wouldn't be able to wear pants without his cock rubbing against the waistband, and that sort of stimulation would definitely get him hard.

If this kept up, he wouldn't even have the safety of his chastity cage to keep him in check. Their current predicament was that they were having trouble getting the damn thing back on after his weekly wash.

"I'm gonna have to force it," Kacchan said, "and bend the damn thing so I can fit it in."

Izuku did his best not to squirm. Closing his eyes, he counted his breathing and tried to keep calm. He was so close to getting it back on. Once the cage was replaced, he would go back to pup mode, and all of his problems would seem farther away. That didn't solve any of them, but right now he just wanted to float free, wanted to stop worrying for a moment about the unexpected changes to his body. Kacchan's grip around his cock was firm, but not the fun, focused grip that meant he was about to get off. It was the squeeze of a man trying to open a particularly pesky bottle of marinara sauce, wringing at it and forcing it to submit.

"Hurts," Izuku whined.

"Well, you're the one with the weird dick," Kacchan growled. "Shit, I think you grew a fucking bone in the middle of this thing."

"And it feels like that bone is breaking. Kacchan, you're gonna break my dick!"

At this, Kacchan let out a frustrated huff and relinquished his grip.

"I guess you'll just have to go without your cage for now," he said.

His tone was nonchalant, as if it was no skin off of his back. Maybe it wasn't to him. But to Izuku, this was the same as telling him he could no longer wear his collar. His cage had become part of himself, an extension of his body. It helped him slip into pup mode, and when he wore it he knew that he was someone special to Kacchan. Owned. Without it, he might as well be naked.

Also, realistically, he knew that if left to himself, he would spend most of his time masturbating. He couldn't help it! Puppies were creatures of instinct. It was unnatural to expect them not to chase what felt good. Even if he knew that his dick belonged to Kacchan, that wouldn't help his resolve– or curiosity– at all.

Upon seeing his distress, Kacchan reached out and patted him on the head.

"Hey, don't give me that look," he chided. "It won't be permanent. I'll have a custom cage made for you."

That was one of the perks of being fabulously wealthy. Kacchan could get someone to make a custom cage, built to absolutely irregular specifications, and have it done no questions asked. For enough money, he could seal lips and stop rumors. It was a fortunate position to be in. But that didn't change the fact that for the meantime, Izuku was unfettered.

"I-I'll try to be good," Izuku promised, even though both of them knew that was a lie.

"If you aren't, we both know what will happen."

Izuku gulped, but he wasn't sure how much of it was fear and how much was excitement.

Silk felt amazing. It was so soft, and smooth, and didn't absorb moisture too well, which meant Deku got to enjoy the sensation of his precum smearing everywhere. And that was just the outer cover. The pillow itself was high end, extra firm, and it held up against his rutting with commendable resistance.

Kacchan was going to be livid when he saw what Deku was doing with his pillows. Not Deku's fault. They smelled so good, buttery and warm like master, and Deku was just so, so horny. His hands were locked away inside his mitts, which meant that if he wanted to get off, he had to resort to humping.

Behind him, his tail wagged triumphantly, tight circles of mischief and joy. This felt good. Really good. His thoughts weren't more complex than that. He had an abstract understanding that this was bad and there would be consequences, but those seemed so removed. Right now, all he was concerned about was chasing the good and taking as much as he could.

The more he rutted, the more the air around him smelled like Kacchan. If Deku focused, he could almost imagine it was Kacchan beneath him, his warm body and soft skin supple as Deku frotted against it. Kacchan always felt good. Deku was sure that if he just had the chance, he could drag all sorts of fantastic sounds out of his normally reserved, grumpy owner. Deku would make him whine, make him whimper, make him squeal–

"The fuck are you doing?"

Deku froze mid-thrust. Instinctively, his tail whipped between his legs, hiding itself, and he felt his ears flatten against his head. Standing there in the doorway was an outraged looking Kacchan.

"Bad. Dog."

This had the same effect as a slap. Deku flinched, jumping off the pillows and rolling over to expose his belly. Tucked between his legs, his tail gave a tentative, nervous wag.

"Nuh-uh," Kacchan responded, "not gonna cut it. You don't get to bootlick your way out of this one."

Kacchan stepped out of the room, but Izuku remained frozen where he was, too terrified to move. It wasn't that he feared Kacchan would hurt him, more… what if he wasn't loved anymore? What if this was the final straw, and now Kacchan just thought of him as a dirty, gross dog? Izuku didn't think he could take it. He was a good dog, and he was determined to prove it, so he stayed where he was, hands tucked up to his chin, stomach facing the ceiling.

When Kacchan finally returned, he wielded an orange spray bottle in one hand. Deku recognized it. They had played around with such a device a while back to discipline Deku. However, Deku was normally so well-behaved that he didn't need any sort of discipline. Except for now.

Raising the bottle, Kacchan growled, "Bad. Dog."

He spritzed Deku. The cold water felt like an open-palm strike, cold and unexpected, and Deku flinched and whimpered.

"You're a disgusting, dirty little animal, you know that?"

Yes, Deku knew that. He knew that he was nasty and weird. He always had been, but this latest transformation had made it more pronounced. If even Kacchan turned his back on him, then he would have nothing, and he felt that like a bone-deep ache.

"I ask basically nothing from you," Kacchan continued, delivering another peppering with the bottle, "other than you obey me. It's the easiest job in the world, and you can't even do that right."

More water came, enough to be a full-blown rainstorm. Deku squirmed on his back, trying to wriggle away. However, as unpleasant as the water was, it did not do much to discourage his current arousal. Once he was worked up, lately it had been hard to get his dick to retreat back into its sheath.

After emptying the contents of the bottle on him, Kacchan strode over and towered above Deku, glaring down at him. The pup whined, doing his best to look innocent and appeasing. Perhaps it worked, because as Kacchan stared at him, his glare eased into something more focused.

"Interesting," Kacchan mused. He reached out with one foot and toed Deku's dick. The man whimpered, his cock throbbing from even that light touch. "You've got a bit of a bump down there. Did you know that?"

Craning his head up, Deku saw that he did indeed have a swell at the base of his cock. Perhaps that was why it was so hard to get rid of his arousal these days, the strange bump catching on the rim of his sheath and preventing him from going back in.

Deku had heard of this. He'd seen furry porn, after all. That right there was a knot.

Both he and Kacchan stared at it, absolutely riveted, for several minutes. It looked like a fleshy ruby, a large knob that was begging to be kneaded. What he wouldn't give for Kacchan's hand to reach out and grip it.

He didn't. He just stood– and watched. His gaze was inscrutable, but with those eyes on him, it was a long while before Deku was at last able to get soft. Deku's new cage came in, and things were supposed to go back to normal. However, even locked up, there was no denying that Deku's downstairs was shifting drastically. Now when he was aroused, his dick would throb, his knot pressing painfully against the walls of the cage. It was painful enough that he usually didn't stay hard for long, and then when he was soft and the pain receded, he could get horny again. It continued in a vicious cycle, and it was killing his sex life. Considering most of his life revolved around his sex life, that was pretty serious.

"Here, we'll just take the damn thing off for tonight," Kacchan said in frustration, unlocking it. "I'm tired of listening to you howl."

Deku whimpered, ears flattening against his head.

The cage came off with a yank, Deku's skin peeling off wetly. The thing was red, although that wasn't unusual. Ever since two sessions ago, when it came out of its sheath it was a bright candy apple red, impossible to ignore. So Kacchan didn't ignore it. More and more, he would reach out and give it a stroke, fascinated with the texture.

"It doesn't even feel like a dick," Kacchan observed. "It's more like some sort of sea slug."

It wasn't exactly a compliment, but Deku still wagged his tail. Any attention from Kacchan was good, even if it hurt.

Even if the touch was exploratory, it still provided him stimulation. Everything in his body felt warm, flooded with the hot heat of arousal. Unbidden, his tongue lolled out of his mouth, long enough now to wave like a banner in the breeze. He was getting fur in more and more places, so these days sweating wasn't enough. When he got worked up, that heat stayed with him, buried under his skin like bottled sunlight.

He wasn't used to getting off from his dick. For so long, it had been off limits. That was part of the way Kacchan owned him– by deciding which parts of his body he was allowed to use, by controlling his pleasure. Rather than feeling more like equal partners, Deku felt even more owned like this. Currently his body was a curiosity for his master's amusement, open for investigation. Along with watching his cock slowly unfurl from its sheath, Kacchan also enjoyed the knot that blossomed at the base. It was a new thing for both of them. Deku had yet to be able to explore it with his own hands, but it burned with the desire to be used, to be buried in something warm. There was no cold more extreme than that of room temperature air against an exposed cock.

He whined and trembled at his master's touch, silently hoping for one sparking, flame-warm hand to wrap around him. None came. There was only Kacchan, touches teasing and so damn light. It was torture, and Deku wanted more.

"Hey, easy there, stay," Kacchan said, giving Deku a light flick on the nose. "No going and trying to hump my hand, okay?"

That was not okay. Deku wanted nothing more than to rub his greasy, yearning dick into Kacchan's smooth palm. He wanted to look into his master's smiling face while he did it, lick inside his mouth and taste him. He wanted his scent all over Kacchan's body, wanted to grind it into the man's pores so that everyone would know Kacchan belonged to him.

The animal inside of Deku did not like to share. The idea of Kacchan going out into the world, being loved and seen by everyone, made something inside him scream. He needed to claim Kacchan, to make sure the man knew–

"What are you growling for, huh?" Kacchan punctuated his words with a light rub to the base of his cock, dancing around the knot without actually touching it. "If you dare bite me, I'm going to start muzzling you."

At the threat, Deku's cock bobbed, the tip glistening with wetness. Yeah. A muzzle. Maybe if they weren't gonna cage his dick, they'd need to cage something else.

Closing his eyes, Deku thought dreamily of the prospect, basking in the continued light touches Kacchan gave him.

It had been a month since their last meeting with Moreau. There had been so many changes recently that the two had been taking their time exploring them. Deku's tail was full and proud now, a curly spiral so profusely fluffy that it looked like a pure orb of fur. His ears had poked up and up, before finally softening at the tips and flopping back down, folding over themselves into neat triangles. They still could twitch and rotate, honing in on sounds, but they were unmistakably the soft, droopy ears of a puppy.

So many changes had dogpiled on top of each other, encompassing basically every part of himself. His teeth were sharper, his tongue longer, his entire mouth pushed slightly out into a pug-sized muzzle. While his sense of smell had spiked, his eyesight was a bit dimmer, colors less interesting than they used to be. Even the bones in his legs and hands were beginning to shift, his fingers slightly shorter than they used to be, thumb pulled higher up onto the meat of his hand. It had gotten to the point where he struggled with buttons, texting, holding a pen– fine motor skills– even without his mitts on.

That was the scariest part: so much of his pup gear was becoming superfluous. Deku hadn't seen his tail plug in months. Likewise, he usually went without mitts or even his knee pads most days. It was simply easier to fall to all fours naturally, spine curving perfectly into position. While he could still walk around on two legs, trotting along on four felt more efficient. There were better smells down here, and he didn't have to worry about what to do with his hands.

He was still a long way from passing as a dog, but likewise– being a normal human was long gone.

"So when are we going in for our next session?" Kacchan asked, reaching out and rubbing the side of Deku's cheek with one foot. He leaned into it, eyes glazing over at the stimulation. It was hard to provide a coherent response when he was getting rubbies. His entire mind sort of flat-lined, a blissful haze of contentment. However, Kacchan had asked him a question, and his doggy brain turned it over, trying to formulate a response. When at last the foot pulled away, he had one.

"I don't know how much farther we want to push it," Deku replied. "I mean, I already have all the features we wanted, right? The tail, and ears, and… the other thing."

'Other thing' meant his new, weird dick. That wasn't a feature they had planned for, but it was certainly one they were taking full advantage of.

Kacchan was silent for a moment, and instantly Deku tensed. He hated disagreeing with his master over even trivial things. Life was better when Kacchan got what he wanted.

Scowling, Kacchan replied, "Right now you're a total mutt, though. You don't look enough like a puppy to be adorable."

Instinctively, Deku's ears lowered. He did not like to be insulted, especially by his master. Especially when he was feeling, for the first time in his life, like he might actually be a little bit… adorable. Like he was finally someone people could find endearing, would want to be around. No longer the weird, quirkless hanger-on.

"My tail is cute, and my ears are cute, and… and Kacchan, when exactly will it be enough for you? When I can no longer walk around on two legs? When I can only bark instead of speaking? Because that might happen if we keep this up!"

Shrugging, Kacchan said, "Look, we're not done until it's done."

"I get to decide what done is!"

This shocked both of them into silence. Izuku hadn't meant to snap like that. Talking back to Katsuki was a habit he had long ago trained himself out of. But this was his body, and Kacchan had promised when this whole thing started that Izuku would get to decide when it stopped.

"Listen," Izuku said, pulling himself up to his feet, "I have been so loyal to you. I have given you every part of my body willingly, even eagerly. But Kacchan… this isn't just my body we're talking about. It's my mind. There are some days, more and more often, where I slip into puppy mode, and it's like a door closes behind me. And every time, I'm afraid when I try to open it back up, I'm going to find out it is locked."

His voice was the careful quiet of confession. For a long time, he'd tried to ignore it, as if afraid that by acknowledging it, he would make something real. But it was real whether he acknowledged it or not, and he had to face that. Something was happening to his mind throughout this process. He was losing a part of himself. Already, he knew he couldn't be fully human again, and that was terrifying and humiliating to admit. Part of him needed to be the dog, to act on impulse and satisfy needs, incapable of restraint. But at the very least… he shouldn't get rid of the part of himself that could still feel disgust, that could raise its head up from time to time and cast him a disapproving stare. Something to remind him that he could be more than just a wild animal.

Kacchan did not share his concerns. In fact, judging from the snort of laughter and the way he rolled his eyes, he found them to be ridiculous.

"Look, even when you're fully in pup mode, you're still you," he replied. "Still shitty Deku, sticking his nose in things, eager to please, annoyingly friendly and curious. So what if you care less about taxes and war and philosophy? You don't need that shit. It's never made you better."

"It's not about whether or not it makes me better. It's about making me human– "

"You sucked as a human!" Kacchan shot back. "Since the moment you were born, you were shitty at it. Couldn't get a quirk, couldn't ever keep up, couldn't even stand up for yourself when it really mattered."

His eyes were dark, scouring Deku's skin like they wanted to leave knife trails across freckled flesh. They'd have to fight through the fur, first. (And the freckles hadn't been visible for a long, long time.)

"Face it, Deku," he spat, "you should have been born a dog in the first place. I'm just trying to set the universe right."

"That's not fair," Deku replied. Even as he said it, he shook. He hated this sick, nasty feeling of arguing. When had it ever accomplished anything? Even on the rare occasions he was right, he never managed to change anyone's minds. They would just blunt force their way into what they wanted.

(For the first time in a long while, Izuku again thought of that alley. It was the first time he had used barking instead of words. If he had stuck to words all that while ago, would things be different now?)

(He had a hard time believing it. Things had always been destined to turn out this way.)

"This isn't about fair."

Kacchan crouched down so he could see eye to eye. With what Deku had become, the only way to get on the same level was to stoop.

"Here are your options," Kacchan said. "You can be my puppy, or you can be a stray. Either way, you'll always be a dog."

Deku didn't have words. All of his reasoning and logic died in his throat, and the best he could do was a whimper. He wasn't okay with this. But as he'd come to realize, him being okay with things didn't really matter. What mattered was what Kacchan felt like giving him, and whether he chose to accept, or he chose to be alone.

Reaching out, Kacchan slid his fingers under Deku's chin, raising his gaze. The dog inside of Deku howled and trembled at having to stare into someone's eyes like that. Then those hands moved on, hooking under Deku's collar and dragging him forward, wrenching a gulp out of him.

"I told you," Kacchan purred, "as long as you're my dog, I'll take care of you."

And then he was pulling Deku onto his lap, hands running over the fuzz coating his body. The pup wanted to take over. It wanted to close its eyes and bask in the warm attention, let itself be spoiled. But as always, the human had to rear its anxious head and mess everything up.

"I don't want to be just a dog," he said, breaking one of their cardinal rules. When he was in pup mode, he wasn't supposed to speak. "I want other friends. I want a life outside of just getting fucked and waiting for you to get home."

A hand clutched the back of his neck, and Deku tensed. Kacchan's arms were not to be denied, strong enough to force his head down despite how he pushed back. At the same time, something was feeling around his tail, searching for his hole. He had been very empty lately, and despite his current predicament, he couldn't help but feel a cold thrill when one finger wormed in.

"When are you gonna learn that there's nothing else for you?" Kacchan asked. "You can fight the animal your entire life, pretend to be human. All it will get you is miserable."

Deku flailed, trying to search for something to push against. With Kacchan's hand on the back of his neck, he couldn't get any leverage. Right now, his hands couldn't grip the pants beneath him for support, his stubby fingers slipping on the fabric.

He could feel Kacchan's erection pressing up into his stomach. The sharp rub of straining denim chafed at him even as Kacchan rocked him back and forth, thrusting his fingers in and out.

"You've been searching your entire life for a calling?" the man sneered. "Well, here it is: you exist because it gives me pleasure."

With pinpoint precision, Kacchan crooked his fingers. Suddenly Deku's world was alight, everything brilliant and twisting around inside him.

He wanted to open his mouth and tell Kacchan to stop, but all that came out was a howl. Lucid thoughts had left him. All there was inside was a deep need, his entire body hollowed out to make room for Kacchan.

"Just stop fighting it, Deku. Let yourself be the animal you are."

Hands pulled out of him, despite Deku thrusting his hips backwards chasing them. And then that hand was at his tail, yanking so hard he saw stars, Kacchan hauling him up by collar and that protruding bit of spine, then forcing him down onto the floor. Deku was able to stand on all fours comfortably, falling into the position like he was built for it. He didn't even try to rise.

There was the one long note of a zipper being pulled down, and then Kacchan's cock was dragging along his back, smearing the green fur with his precum. Deku wanted that member inside him, was aching with the emptiness.

"Stay down and do what you're made for," Kacchan ordered.

Deku couldn't fight him. No, fighting hurt. Obeying felt good. It did something to the inside of his brain, made everything feel easy and smooth, no more sharp edges to cut himself on. No more decisions that he would only get wrong.

"Stop pretending to be something more than you are. Just admit that at your core, you're a selfish, stupid animal."

Kacchan's voice was a long growl of pleasure, feral enough that it sparked something in Deku. Whatever that voice demanded of him, he would give. He would be good. After all, it had authority and power he could only dream of. It was alpha.

"Once you do that, everything will be easier."

Thrusts, up and down, dragging along his spine. Deku rolled with them, curving himself up to meet it. He was getting soaked with Kacchan's seed, marked with it.

"After all, it worked for me."

Kacchan came on his back, and Deku's fur was dense enough now that it stayed on top, like water unable to soak into wax-dipped fabric. The warmth was right there, but it couldn't even get skin deep. The fur prevented him from feeling anything directly. He made no move to shake it off, instead lying there on the floor, panting. Panting like a dog, his tongue lolling, entire body trembling with the force of it.

But he would not be allowed time to recover. Kacchan was interested only in moving at his own pace, and he didn't want to wait for pokey Deku to make up his mind.

"So what will it be?" he asked.

Deku craned his head up and up, so far that his collar dragged against his Adam's apple. Kacchan leered down at him, awaiting his answer, confident he already knew what it would be.

"Are we going back to the doctor?"

It was now or never. Deku had a choice to make: be Kacchan's beloved puppy, or be an outcast and a freak.

He opened his mouth and gave his answer.