DXD: Biokinetic Devil

A pile of books surrounded Julius Mercer as he read in a library. All around him, one could see that the titles of each book were related to medicine. Titles such as "The Devil's Anatomy" and "A Beginner's Guide to Devil Medicine" were examples of what the eight-year-old was reading.

He had well-groomed short black hair that parted in the middle and bright green eyes. He was dressed in a white button-up shirt and black pants as he sat in the library, pouring over the medical books with a fervor that contradicted his age.

'I think I'm ready to at least try some small things,' Julius thought to himself as he closed the book he was reading.

The library he found himself in belonged to the Sitri Clan within the underworld. His parents had both been reincarnated devils; his mother was in Lady Sitri's peerage as a pawn while his father was a rook in Lord Sitri's peerage. His mother had been a magician before she was reincarnated while his father had been a human with a physical enhancement Sacred Gear.

Julius had grown up within the Sitri household, although he'd hardly interacted with the main members of the family. He was a Mixed-Heritage devil, someone who was born from the union between either a reincarnated devil and a pure-blood, or two reincarnated devils. His kind occupied an awkward place in devil society; they weren't viewed as negatively as reincarnate devils by pure-bloods, but they also lacked the backing that came with being part of peerage so they largely fended for themselves as lower-middle-class citizens.

He was lucky to be allowed to live with the Sitri's, even if he was relegated to a guest house separate from the main estate. Especially with his parent's circumstances, they easily could have just sent him away, but they'd allowed him to stay and study in their halls.

Cleaning up the books around him, he began to make his way through the large, open halls of the main Sitri estate. There was the occasional maid who passed him and who'd give him a small smile and continue on their way. As he was walking, he ended up seeing Sona Sitri, a short girl with her black hair cut in a bob and glasses, making her way in his direction.

"Heiress Sitri," Julius nodded his head.

"Julius," was the curt reply as she continued on her way past him. The two were the same age, and there had been some attempts at getting them to be friends when they were younger, but he'd become occupied and their differing stations made it difficult in the first place.

He finally exited the main house and made his way along a stone path. Finally coming to the door of a smaller building, although still large in comparison to most houses, he opened the door and stepped in.

Walking through the hallway, he quickly made his way to his destination and opened the door, stepping in and taking in one particular thing in the room.

Laying in bed, sound asleep, was his mother Hope Mercer. She had short, silver hair and looked emaciated. Making his way over to his mother, a green sigil formed over his palm as he touched her, casting a diagnostic spell.

The spell scanned his mother's body, giving him information about her condition and he couldn't help but sigh as he got the information.

"Still no changes," Julius muttered to himself.

Hope Mercer had raised him for six years before she came down with the Sleep Disease. His father had died in a skirmish with exorcists, so she had been his only parent growing up. Sleep Disease was a unique disease devils could get, seemingly completely at random, that caused them to fall into a deep sleep, unable to be awoken. Their life force would be slowly drained away as they became weaker and weaker the longer they slept until they eventually died. The time it took varied from case to case, and there had been no cure found.

This was the reason Julius spent so much time in the Sitri library, reading medical books. He'd delayed his practice in using his demonic power for one single purpose; to create his own magic that would let him heal his mom. Most devils started actively developing their magic around age six. He knew for a fact Sona had begun learning to use her clan's inherent water manipulation at that age. Instead, he'd spent the last two years pouring over medical journals and getting as much information as he could so he could begin practicing.

Stepping away from his mom, he made his way out of his room and into a greenhouse in the back of the house. He quickly found a simple potted plant and sat down at a table, setting the plant down in front of him as he ran his hands along it.

'Okay, demonic power is the power of imagination. I've done as much research as possible, now I just need to let my imagination fill in the gaps and let me create the magic.'

Julius concentrated, casting the diagnostic spell once again and getting a complete picture of the plant's biological structure. The green sigil continued to float over his hand as he focused, trying to create a simple change in that structure.

It took him thirty minutes of trying, and he was only able to succeed that quickly because of how long he'd been preparing for this, but he finally managed to do something. The formally green plant shifted, changing to a light blue in front of him.

Julius panted in excitement looking at the plant in front of him. "It's a small change, but it's possible. I just need to practice."

The next couple of hours were devoted to just working with his magic, developing it as much as he could in that short time. He made the plant change through a variety of colors, he made certain leaves elongate and shorten and changed the shape of the various parts of the plant. He was focused on cosmetic changes, knowing it would take time and practice to even begin to change the internal structure of a living being.

As the artificial sun that floated in the underworld sky began to set, Julius finally stopped and returned the plant to normal. Making his way out of the greenhouse, Julius returned to his room and lay down in bed. It was early to be going to sleep, especially for a devil, but he needed time to mentally go over his plans.

'I'll continue with plants for now, but eventually, I'll need to move on to devils if I want to be able to figure out how to heal the Sleep Disease. Maybe in a year or two, I can try to apply to assist at the Sitri General Hospital. It's said to be one of the most advanced medical facilities in the underworld after all. I can see how different things affect patients, and after maybe I'll apply to the Agares Hunters.'

The original Agares was known as the devil "to make deserters return." This had ended up being continued by his descendants, and an association was formed under their banner of devils specifically sent to hunt down stray devils. Most pure-blood devils sent a few of their peerage members there for a year or two to train in active combat, and a lot of younger mixed-heritage devils did it for work, so it wouldn't be unusual for me to join.

If he did become a Stray Hunter, he could use his powers on devils that nobody cared about and without consequences. He'd need test subjects, and they were the only group of devils nobody would care about if they were killed.

If he was going to do that though, he would need to get strong. He had a start on his demonic power now, so he'd devote every waking moment to improving. He'd become strong, and he'd learn at the hospital so that he could one day cure the Sleep Disease.

----

It'd been a couple of years since then and Julius was now ten years old. He'd spent the last two years practicing on the wildlife in the greenhouse, moving on from plants eventually and learning to manipulate the animals that lived there as well.

He was currently once again sitting in the library, reading up on the various kinds of diseases and illnesses that occur in not just devils, but all the races that were documented. 

He was mildly surprised when his concentration was broken by the sound of the library door flinging open and then slamming shut loudly. He sighed as he got up and made his way through the maze of bookshelves to find out what was going on. He mostly kept to himself, and while there were times when another member of the household, whether it was Sona or a member of the Lord and Lady's peerages, would come to the library, they mostly kept quiet and to themselves.

Julius found a panting Sona leaning up against the door to the library. It seemed that she had been running from something or someone, as she had her ear pressed against the door and was trying to listen to the other side.

"Sona, come back. Why'd you run off?" he could hear a voice he had to take a moment to place.

"Running from your sister Heiress Sitri?" Julius asked as he made his presence known.

Sona turned around quickly but calmed down upon seeing that it was him. Before his mother had fallen ill she'd made sure he was informed on how he was supposed to act around pure-blooded devils. Julius found the whole thing a little ridiculous and for a while it made him angry that he had to be so respectful to them, but until he was stronger it was best to act as he was expected to.

Sona quickly composed herself, the stern gaze she took on looking somewhat odd on a ten-year-old. "I was simply checking up on you, Serafall just happens to be here."

Julius chuckled lightly at her lie. "Well, as you can see I'm just reading. Feel free to spend time with your sister."

He started to walk back towards his chair, sitting down and opening the book he was reading, but Sona didn't leave, instead taking the seat across from him.

"Perhaps it'd be best if I made sure everything is well in hand," she said seeing him look up at her. It was amusing seeing her try so hard to be prim and proper while pretending like she wasn't just hiding out from her sister.

They sat in silence for a little while, only the flipping of the pages of Julius' book echoing in the library before Sona addressed me again.

"Would you care to play a game?" she asked as she held up her hand. The Sitri sigil formed in the air and a chess board appeared on the table in between us.

Julus set his book down and considered it for a moment. "Sure, I haven't played all that much, though."

"That's fine, it never hurts to practice."

She quickly set the board up as we began to play a game. He didn't particularly enjoy chess, although most devils learned how to play at the very least since the evil piece system was based on it. 

It was quickly apparent that Sona was going to trounce him. She was too good, and despite his best efforts, he was quickly put in checkmate.

"Again?" Julius asked, despite his desire to continue his research. He was a competitive person, and the fact that he'd been beaten so soundly grated on him.

Sona nodded, quickly setting up the board as the game began anew. This time, though, she decided to talk to him while they played.

"How is your mother?" Sona asked him.

He considered her question for a moment while he decided his next move. "She's still the same, although she's getting weaker."

"I'm sorry. Is that why you spend so much time in here?"

That comment surprised me a little, and it must have shown on my face. "We do care about you, you know? Your mother is a member of my mother's peerage, even if she's fallen ill. I know we didn't hit it off like our parents hoped, though."

Julius wasn't sure how to feel about what she said. He'd never really cared that he didn't talk to anyone in the house since he was focused on trying to become strong enough to cure his mother. Their parents had tried to set them up as friends when they were little, but he'd thrown a tantrum when it'd been said he could join Sona's peerage when they grew up. His reaction might've been overblown as a four-year-old, but he still felt the same way. He had no desire to join a peerage.

"It's the reality of our stations. A friendship between us would be built up for me to eventually join your peerage."

Sona hummed lightly as she played her next move. "You don't have to join my peerage to speak with me, Julius."

"I...guess that's true. I'm busy with my studies most of the time though."

"And I'm busy with my duties as heiress, but if we find the free time I wouldn't mind playing a few games," she said, indicating the chess board.

"You mean beating me a few times," he commented as he moved his piece.

Julius was surprised to see a grin form on Sona's face as she played her piece. "Checkmate."

He sighed, knowing it'd probably continue this way if they played another game. He'd have to practice more before he had a chance at beating Sona, and his competitive spirit refused to let him accept the current state of affairs.

"Okay Heiress Sitri, we'll play when we have the time."

"Sona, call me Sona. At the very least when we play," Sona said, adjusting her glasses as she stood up from the chair.

"Very well, Sona," Julius replied, the name feeling slightly awkward after all the etiquette his mother had ingrained into him.

----

Since that day, Julius and Sona would occasionally play a few games of chess. He also started to finally put up more of a fight, although she would still beat him every time. It was starting to become an obsession of his to beat her. He still focuses mainly on his demonic power, and another year passed in his practice before he was finally ready to go study at the hospital.

Standing outside of Lord Sitri's study, Julius knocked lightly. He'd had the meeting scheduled in advance, so he knew he wouldn't be interrupting anything. The door swung open, a servant moving the side and allowing him to enter the room.

Lord Sitri was a tall man, with violet eyes and black hair. His features had become set in a grim countenance, and he tended to give off a very serious vibe.

"Greetings Lord Sitri, thank you for meeting with me," Julius said, bowing lightly to the man.

Lord Sitri smiled at him, giving the boy an appreciative nod. "Certainly, your father was a member of my peerage after all. I think I have an idea what this is about."

"I'd like to be sent to one of the Sitri Hospitals to study medicine," Julius said.

"We've all seen how hard you've been studying medicine, I don't think it'd be an issue to send you to apprentice under someone there," Lord Sitri said, surprising Julius somewhat. He'd assumed he would just be sent to observe, or work as a nurse, but an apprenticeship under someone would help him a lot.

"Don't look so surprised, it's a simple enough request and you've never asked anything of us. Your father was a good devil, as is your mother. I'm assuming she's the reason you want to study medicine?"

Julius nodded his head in response, and Lord Sitri looked thoughtful for a moment. "Were you aware that my grandfather also suffered from Sleep Disease?"

"What?" Julius exclaimed, his eyes widening in surprise as he forgot himself for a moment. He hadn't known that at all, he was pretty sure it wasn't well known by most of the underworld as well. 

"Yes, he came down with the disease and eventually passed. It isn't known why the disease occurs, nor if it is hereditary, but it would be good if a cure was found. Just because no one has done it so far doesn't mean it's not possible."

Lord Sitri stood up, moving to one of the bookshelves that lined his office and searching through them for a moment before he found the book he was looking for. Taking it from the shelf, he walked over and handed it to Julius.

"This is the research that our private physicians did on the disease when my grandfather came down with it. If you're going to be studying it, best to not go over things they've already looked into."

Julius held the book gingerly, stunned by Lord Sitri's kindness. He had hardly interacted with the man, but he'd always come off as a cold individual and excessively stern.

"Thank you Lord Sitri. This means everything to me," Julius said, resisting the urge to start reading the book right away.

Lord Sitri moved back to his desk, sitting down once again. "At the end of the day, everything in that book still ended up being a failure. Do your best Julius, I think everyone in the underworld would be happy if that accursed disease is destroyed."

Julius said his greetings and left the room, hurrying back to his house. He passed by the sitting room as he ran, which contained Sona who sat across from a girl with long red hair and blue-green eyes.

"Julius?" Sona said in confusion at seeing him run past her.

"Sorry Sona, need to do something," Julius called out as he ran, completely forgetting any kind of etiquette. His mother would've reprimanded him for it, but he was too excited to care. He hardly even took note of the other person in the room as he ran out the door, returning to his house to begin reading. 

"Well that was something," the red-haired girl said with some amusement.

Sona just shook her head, returning to the game of chess the two were playing. "He had a meeting with my father today, I'm guessing it went well."

The girl accepted her answer, a look of concentration on her face as she focused on the game the two were playing. She moved her piece, and Sona responded almost immediately.

"Checkmate Rias."

Julius had long left the building, but he could still hear Rias' frustrated yell echo outside. He chuckled to himself, recognizing the emotion in that scream.

"One day Sona, you'll be on the receiving end of that feeling."