Just a note, this is is an alternate universe kind of thing that's still in the canon universe. The only differences are the fact that soulmates exist here (I'll elaborate on that in a second), and that the students already stay in dorms (I'm pretty sure that's not a thing in the anime? I dunno man)
This soulmate AU doesn't really need explanation, as I explain it within the story. If you get confused, I may elaborate on it later.
On a final note, there will be some background Kiribaku/Bakushima in here, just be aware.
At precisely 3 in the morning, Midoriya Izuku was staring up at the ceiling, absentmindedly tracing the outline of a large mark on his arm with his fingers.
(At the same time, in a room not far from his own, Todoroki Shouto was doing the same with own mark, or where the mark would've been anyway.
The scar around his eye served as a constant reminder of why he had chosen to forfeit the use of his fire, along with providing the knowledge that someone, his soulmate, would touch it, perhaps because of the same fascination others had with it. Before the boiling water had hit his skin, there had been a mark resembling fingers gently dragged along the skin under his eye, and he had been confused as to why someone would touch there of all places, but the reason later became obvious.)
Midoriya's mark, the one around his arm, took the shape of a hand, slightly larger than his own. It wasn't an uncommon place for people to touch, so he knew he'd likely never see the moment coming. Ever since arriving at U.A., they'd done a lot of training, allowing for countless moments of his classmates grabbing his arm. Not once had he felt the rush that was talked about so often, nor had he witnessed the black of the mark suddenly change into a plethora of colors, another telltale sign that 'hey! that's your soulmate!'.
He wasn't too concerned about it, he was only in highschool, so he had plenty of time. He was just jealous in a sense, he'd seen people meet their soulmates in middle school, and he was plain curious on who his would be. It was frustrating, having a mark that got touched painfully often, while he'd seen others with the kind of marks that only one person would ever touch.
Soulmates and quirks. They were the kinds of things Midoriya would stay up thinking about, depriving himself of the sleep he knew was important on the road to becoming a hero.
(Unbeknownst to him, Todoroki stayed awake thinking about the exact same things.)
Arriving to class sleep deprived was never the best idea, especially when you went to school at U.A. Sparring was the focus of much of the day, and Midoriya was paired up with Iida, someone who was always awake and ready for anything class threw at him. While Midoriya was certainly awake at this point, his movements were more sluggish than usual, and Iida was the one going more on the offensive.
At one point, one of his feet had gotten caught on the other, causing him to stumble backwards and fall. He shut his eyes at the moment his back made contact with the ground, opening them a moment later.
He looked up to see Iida reaching a hand out to him, speaking as he did so, "Midoriya! Are you alright? You seem distracted, you are getting a full 8 hours of sleep, right? Getting enough sleep is essential to productivity during the day!"
Midoriya grinned sheepishly, taking the hand, "Yeah, I'm okay! I got a little less sleep than that but..." he let out a slight laugh, "It's alright, I'll make sure to go to sleep earlier tonight!"
He brushed himself off, and placed himself back into sparring position.
As Iida did the same, he smiled, "Good, it's important to take care of yourself, remember that!"
Midoriya was thankful for Iida's concern, and perked up slightly, focusing more on the sparring, and daring to take the offensive more often than he had previously. His facial expression changed into one of determination, and the sparring session ended up being quite productive for him.
He was so focused, he had failed to notice a certain pair of heterochromatic eyes watching him.
Despite Iida's insistence, Midoriya didn't get 8 hours of sleep during the following nights. The mark on his arm was just so distracting, and always sent his mind into a never-ending spiral of thinking.
Some nights he'd try to coax his mind into a state of relaxation, getting up and out of his room to get a midnight snack, or have a cup a of tea. Sometimes, as he'd enter the kitchen, he swears he'll see a flash of red and white hair leaving the room. It makes him wonder if he's not the only one who can't get to sleep.
(He's certainly not, but Todoroki prefers not to make conversation with the others, and leaves the kitchen whenever he sees or hears Midoriya enter.)
But, as the moment always went by so quickly, he could never be sure that he really saw it. He had tried to make his entrances quieter, in hopes he could confirm his suspicions, but he never saw anything more than the back of the person's head. Eventually he had decided that he was, in fact, not imagining things, and he really did keep seeing someone, but he still wished he could at least talk to the person.
The person, made obvious by the hair, was Todoroki, Midoriya soon realized. The wish to talk to the person only grew when he realized this, as Todoroki was one of the only people in the class he had never really spoken to. The boy was secluded, and had made it clear he had no intention of making friends with anyone, let alone Midoriya. It came as no surprise when he'd quickly exit the room as Midoriya entered.
(Sometimes, however, Todoroki would hesitate for a moment and wonder whether he should allow himself to stay, before inevitably going back to his room.)
Midoriya's wardrobe consisted mostly of shirts that had sleeves, so his mark wasn't usually terribly obvious. However, for class, when they'd need to change clothes (today was one of those days), the black mark was there for all the boys to see. Sometimes, Kirishima would mention something about it, a joke of some sort. As the mark was still visible, everyone knew he hadn't met (or at least, hadn't been touched) by his soulmate yet.
He knew many of the others hadn't either, as he had just glanced around, seeing several people with the marks still on them.
It was the first time he'd really taken the time to see just how many of his classmates were possibly in the same boat as him. He was, perhaps a bit selfishly, relieved when he saw that most people hadn't been touched by their soulmate thus far.
There were exceptions of course, those being Bakugou and Kirishima (whom everyone suspected were soulmates), and Todoroki.
The latter was already someone he was intrigued by, and seeing a lack of a mark intrigued him even further. Todoroki wasn't someone who fraternized with the others, and he'd never seen him touch anyone aside from in training. Midoriya figured that it was likely Todoroki's soulmate was someone who didn't go to U.A, but he still had doubts about it, though he was unsure as to why.
He soon realized he was staring when Todoroki turned and looked at him, giving him a cold, questioning look. He stared for just a moment longer, before turning away, his face flushed.
(The look had softened, just as Midoriya turned away, and Todoroki silently hoped the look hadn't seemed as cold as it likely did.)
He scolded himself for looking for so long, and finished slipping his shirt over his head as he left the locker room alongside his classmates.
He took a moment to glance back at Todoroki, who had turned away again, and realized for the first time that he was the only one of his classmates that had never touched his skin.