Mugen Train

"Before we get started… demon-san," I thumbed at my nichirin blade, "do you know what they used to call me?" 

Akaza smirked, "I do not care human, you are beneath me, no amount of power you have could ever hope to defeat me." 

"Hmm," I shook my head, "they called me Kishin." 

Akaza sneered and took a combative stance, behind me Kyojuro and the trio of newbie slayers tensed at the aura radiating from Akaza. 

"That doesn't matter though, you're not even worth me drawing my sword." I dismissed him with a scoff. 

Akaza didn't reply, he rushed at me in intent on crushing my head. I simply leaned and let him fly past me. He corrected himself mid air and launched a kick. I dodged his strike again making him grin evilly. 

"So you have some skill, that will not be enough to beat me. BLOOD DEMON A- URKKK." 

I landed a spinning back kick that shattered every bone in his upper body, I felt his internal organs explode as I sent him flying away. 

"Rule number one…" 

"Never announce your attack!" Kyojuro finished for me with a proud look. 

I turned to him, "Don't think I haven't forgotten about you Kyojuro. Using a jutsu that I haven't taught you properly yet…" 

Kyojuro laughed sheepishly, "Hehe, sorry Uchiha-san, I got carried away." 

The three newbie demon slayers looked at him in shock. 

"Jutsu?" Tanjiro asked in confusion. 

"Oh right, Uchiha-san taught Koc-"

"DON'T IGNORE ME!!!!" Akaza roared as he attacked me again after recovering from his injuries. 

I blocked his punch with Ryujin Jakka's scabbard and looked at him with disdain. Locking eyes with the demon I pulsed some chakra into my Mangekyou Sharingan. 

"Tsukiyomi." 

Akaza and I reappeared in a world with a red sky. The colour bled out of everything and an eerie red moon rose. 

Akaza looked around in panic, he tried attacking me but found himself bound to a stone pillar. He shouted profanities at me as he struggled to break free. 

"Release me human! Let me pulverise your head!" 

"You poor poor demon, you have no idea how outmatched you are." My voice echoed through the Tsukiyomi world. 

Slowly Akaza stopped struggling when he realised it was futile. I slowly walked over to him, my steps reverberating through the empty world. Slowly drawing Ryujin Jakka I looked at him with a tilted head. 

"I wonder how long it will take for you to break?" 

"What?" He glared at me. 

Instead of answering I stabbed him in the gut. He grit his teeth, while glaring at me. 

"In this world I am god, which to me is quite funny since I really am God even outside of this world. Imagine that, a God taking a vacation and using powers he granted himself to become god in an illusionary world." 

"What are you talking about human?" Akaza retorted with an angry look. 

"Ah, forget about it… where was I… oh yeah, edgelord simulator," I coughed and resumed my rendition of Itachi's iconic use of his genjutsu, "in this world I'm god…" 

I turned Akaza back into a human in the Tsukiyomi world. Akaza seemed to panic when he noticed the change in his body. 

"What have you done human!" 

"Hmm? Oh, I've turned you back into a human. Now, let's continue." 

I stabbed him again, this time he didn't have demonic powers, so the pain was undiluted. Akaza screamed as my sword cut into his body. 

I created more pillars with more clones of Akaza in his human form. From the ground more clones of me also emerged, each armed with identical swords. Each clone stabbed into an Akaza again and again. More clones appeared and also stabbed at the screaming former demon.

"You're stuck in here with me for the next seventy one hours, fifty nine minutes and fifty nine seconds."

Akaza continued to scream.

In the outside world, I looked at Akaza who had frozen in place. Hardly a second had passed since I trapped the demon in my Tsukiyomi. Akaza screamed before collapsing on the ground, blood leaking from his eyes, ears, nose, and mouth. 

"What did you do to him?" Kyojuro asked. 

"Same thing I did to Sanemi, only I tortured him for three days straight." I replied casually. 

Turning to the other Slayers who were gaping at me I shrugged. 

"What? He's a demon, he's killed countless people." 

"But… you could have been more merciful." Tanjiro said softly. 

I turned to the young boy, "Tell me, would you show the man that murdered your family any mercy?" 

Tanjiro's eyes widened, I saw conflict behind his eyes. He was clearly and inherently pure soul, yet a part of him wanted to destroy the person responsible for his family's death. 

"I- I would try to understand him." 

"Some people don't deserve that kind of mercy." 

"Bu-"

"Kyojuro, take them and go finish helping the civilians, I'll remain and wait for the Kakushi to arrive, I think Ubuyashiki will be pleased to learn that we've captured an Upper Moon." 

Kyojuro understood that I wasn't going to entertain a moral debate, nodded and ushered the others away. I looked over to Akaza's comatose form before turning to the nearby trees where I sensed a presence lurking. 

In a flash of lightning I appeared before a kindly looking woman and a young boy. The young boy jumped in front of the woman defensively and prepared to fight. 

"Yushiro don't, he's beyond any of us." The woman calmly spoke even though she was clearly terrified. 

"Lady Tamayo, he's one of the Hashira, he's dangerous!" 

"Yes and if he wanted to kill us he would have already done so." She replied in the same calm tone. 

"Indeed," I crossed my arms, "you're different from the other demons. I take it you're not with them?" 

Tamayo, as the demon boy called her, shook her head. She maintained her air of calm, while also remaining cautious. 

"Muzan turned me against my will, he tricked me and forced me to become a demon. Since then I have freed myself from his control and strived to find a way to defeat him." 

I hummed, "Control you say?" 

She nodded, "All demons are under his control, save for a rare few that can resist or escape. Demons are created with his blood after all." 

'So they really are basically vampires.' I through to myself. 

"So far I have met only one other demon who he cannot command, that boy's sister." 

"The reason for that?" 

"I believe that it is due to how she was transformed and her own will power, I have never met a more determined individual than her." 

Yushiro looked between Tamayo and I, clearly displeased with all the information she was sharing with me. I glanced at him briefly, and leaked out a fraction of my Killing Intent. 

"Have something to say boy?" 

Yushiro froze in fear, Tamayo was also affected but she fought through it and gave him a glance. Yushiro looked away and I pulled back my aura. 

"I apologise for Yushiro, he is quite defensive of me." 

My gaze lingered on the boy for a second longer, I enjoyed watching him squirm, finally looking away I turned back to Tamayo. 

"I understand, why are you here though, if you're not with the demons." 

"I came to observe, and to help." 

"I see."

"Before you take him away, would you mind if I took some blood from Akaza?" 

I raised an eyebrow, "Why do you need it?" 

"For my research into turning demons back into humans again, I need the blood off of the strongest demons." 

I could easily turn demons back into humans, at least I could if I wasn't set on being immersive. Here I was just a regular human Demon Slayer, I wasn't going to go around using my divine powers just yet. 

Technically I had already broken that rule by giving Kyojuro and the others access to chakra but that was a minor change in comparison to outright changing someone's biology. 

"Very well, I will allow it. Keep in contact with me, I shall send one of my ravens to accompany you so that we may contact each other." 

To the two demons surprise a raven emerged from my seemingly empty sleeves. The raven perched itself on Tamayo's shoulder before croaking at her. 

"Just tell it what you want to tell me and it will convey this message no matter where or how far I am." 

Tamayo nodded, I glanced at the raven making its eyes flash red as my Sharingan appeared in its eyes. Tamayo looked at the bird curiously but then yelped in shock when it promptly shoved itself down her throat making her gag. 

I fought back a chuckle when Yushiro rushed over to her side trying to yank the raven back out only for it to disappear completely. 

"You! What have you done to Lady Tamayo?!" 

I shrugged, "Nothing, I just made sure she'll always have a way to contact me." 

Tamayo was gasping for breath, she looked at me with teary eyes and an accusatory gaze. 

"You did that on purpose." She gasped. 

[Scene Break]

I hummed a tune while I walked back to Akaza who was still unconscious and slightly foaming at the mouth. The demon looked like he had a seizure, if demons could even have seizures. 

Grabbing the demon by the leg I dragged him over to where everyone else was at, I had no concerns, he posed no danger to anyone. Not after what I had done to him for three days in the Tsukiyomi world. 

Stabbing, burning, making him listen to Justin Bieber's 'Baby' over and over again while I summoned furries in bdsm gear to perform an interpretive dance. 

Even I myself felt a little dirty after that. 

Kyojuro and the others had gathered by the civilians and were checking on them thoroughly. Some had minor scrapes and bruises but nothing too serious. 

The Flame Hashira looked up at me when I approached. He glanced at Akaza's unconscious body. 

"Aren't you concerned that he'd wake up and hurt someone here?"

"Nah… I'd win." 

"What?" 

"Never mind that, where are the Kakushi?"

"I sent out my Kasugi crow out after you sent us off, they should be here any moment." Kyojuro replied. 

Just as he spoke, over a dozen masked Kakushi appeared, they were slightly out of breath as they had just ran from wherever they were stationed. 

The masked individuals started administering first aid to the civilians while a few looked over the injured Tanjiro. Kyojuro had only taken minor injuries that he didn't think were serious so he dismissed the Kakushi trying to help him. 

Inoko was making weird noises behind her mad while she looked in my general direction. I turned to her and tilted my head. 

"I forgot to ask… what's with this one?" I motioned towards the boar masked girl. 

Zenitsu answered for the trio, "We found her in the mountains attacking other slayers." 

"Err what?" 

"I was relieving them of their swords." Inoko stated proudly. 

"So you stole from them?" 

"I- I did not!" 

"Sure sure, and what's up with the mask?" I asked while dismissing her denial with a wave of my hand. 

I could have sworn that she gained a tick mark on her mask. She angrily rushed at me while drawing her swords. 

"You wouldn't understand it you damn pretty boy!" 

Kyojuro held her back, Tanjiro smiled sheepishly from where he was being treated. Zenitsu had paled after seeing the girl rush at me. Clearly he thought I'd attack them now. 

"I'm guessing it's some sort of keepsake? Something to remember someone or something by?" I prodded. 

She huffed and stopped trying to attack me, "It's for my mother." 

"Your mother was a boar?" I raised an eyebrow. 

Obviously I had put two and two together but it was fun riling people up so I kept teasing her. From the little information I was given and the things I observed, Inoko was another victim of a demon attack. 

He was probably just an infant when it happened, her real mother had distracted the demon and led it away from where she had hid her infant daughter. 

My guesses were that Inoko had been hidden by the mountain that Tanjiro and Zenitsu had found her at. There she was raised by wild boars, hence why she referred to the boar mask as a homage to her 'mother'. The real question was; what was the mask made out of. 

It looked realistic enough and seemed to be made out of actual fur. Though I very much doubted that Inoko could have and would have skinned one of the boars that raised her. 

"What do we do now?" The blond haired slayer asked Kyojuro who looked over to me. 

Shrugging I turned my attention to Akaza, who I was still holding by the foot. 

"Kakushi, please take this demon back to my home," I slapped a piece of paper on Akaza's face, "there, that's a seal that will ensure that he doesn't wake up any time soon. Also…" I paused before taking out a length of rope from my seemingly empty sleeve, tying up the demon 

Everyone looked at me strangely, I had tied Akaza up in a standard Shibari pattern. (AN: Japanese Bondage Style)

"What? I think it's funny." 

"Pervert." Inoko muttered.

I ignored her, turning to Tanjiro. I addressed the young boy, "Kamado Tanjiro, if you wish to become stronger, come to the Solar Mansion." (AN: Calling it the 'Sun Mansion' doesn't quite have the same ring to it.)

"Are you going to teach him Jutsus too Uchiha-san?" Kyojuro asked.

I nodded, "That as well as a breathing style that will suit him more." 

"A new breathing style?" Tanjiro looked at me curiously. 

"That's right, it will be familiar to you, but at the same time something completely different." 

Tanjiro nodded, his determination shining in his eyes. Inoko pointed at me and loudly shouted;

"Uchibara teach me too!" 

"No." 

"…" 

"Nani!!!" 

[Scene Break]

The Kakushi had quickly transported Akaza to my home and base. I had them toss him into my dungeon that I built under the house. Inscribed on the walls were various sealing arrays that I tweaked to be able to affect demons.

Akaza was still bound and unconscious with the sealing paper slapped onto his cheek. I had contacted Tamayo and informed her that if she wished to collect Akaza's blood, that she would have to come to my home. 

I didn't plan on revealing her existence to the Slayer Corps just yet. I had no idea how a bunch of zealous Demon Slayers would react to a friendly demon. 

She had promptly responded, she would be arriving in two weeks, I had offered her a place in my home. It was much safer than where she was originally staying. Especially since I placed a bunch of intent based wards on the perimeter. 

Wards that could vaporise intruders or even turn them inside out should they come through with malicious intent. 

"Akimitsu-sensei, I already know the Hinokami Kagura, why are you having me perform it over and over again?" 

I turned my attention back to Tanjiro, who I had now been training for nearly a week. He had accompanied me back along with Inoko and a reluctant Zenitsu who kept muttering something about 'not trusting the guy with evil red eyes'. 

I had placed the blond slayer in a genjutsu that lasted for a week. Mainly because I thought he needed to give his balls a tug, but also because I saw the potential in him. I had heard he had defeated a handful of demons despite being a cowardly type. 

I had learned that he was 'asleep' for most of these, prompting me to investigate and find out that he actually was pretty skilled, only he was too cowardly to act. However whoever trained him had trained him so well that his body reacted instinctively when he was unconscious. 

"Because, I said so." I replied to Tanjiro who facefaulted. 

"Gaaah! Uchoka Kuchihana! Fight me!" Inoko shouted from where she was, that being tied to a tree upside down. 

Her mask had fallen off revealing an unbelievably attractive face. I had told her that if she managed to free herself that I'd fight her and teach her the Uchiha Kenjutsu style. 

"Also is it really necessary to tie Inoko-san to a tree?" Tanjiro looked at her in pity. 

"Yes, now, continue… form 6." 

Tanjiro jumped at my half shouted command and performed the kata. I continued to watch him while Nezuko prodded an unconscious Zenitsu.