I'm jumping on the Soulmate AU train… I just can't help it. So, here it is! The soulmate fanfic that no one probably wants to read!

Disclaimer: I don't own My Hero Academia

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When They Were Soulmates

Chapter 1

When Izuku was four, his quirk didn't manifest like his best friend Bakugo's, and so many others did. In fact, he was told it never would since he was just a speck in the twenty percent of the world that was unfortunate enough to be born 'quirkless'.

He remembered asking his mom if he could still be a hero, and her crying into his hair as she simply said: "I'm sorry, Izuku". Over and over those words played in his head, but he never gave up hope that a miracle would happen someday.

When Izuku was five, something did appear, but it wasn't the quirk he'd hoped for. It was a painful mark on his left ribcage that had caused him to scream for several hours afterward. His mother did her best to quell her son's pain and fear as she soothed him. Inko cried into his messy locks again, but this time, she'd said: "It's a gift, Izuku". From then on, he wondered what she meant.

When he'd finally calmed down, and the burning had stopped, he examined the area in a mirror. Etched onto his skin was a black heart with a crack running straight down the center. To him, it looked like one of the tattoos he'd seen on bad guys, and at first, wondered how a gift could be something like that. So, he said so to his mother, who simply smiled and said she'd explain when he was older.

But, his mother couldn't wait as long as she'd hoped. Almost every day, Izuku would start to cry when the mark burned, sending waves of pain through his little torso. She'd hold him quietly, and rock him back and forth, telling him it was all going to be okay.

When Izuku was six, Inko had enough and sat him down after a particularly long crying session. "My poor baby, does it still hurt?"

Midoriya shook his head, sniffing. "No, but why does it keep burning like that? You said it was special, that it was a good thing, but it keeps h-hurting me!"

"Oh, Izuku… that's a soul mark you have, and it is very special. Soul marks are even rarer than not having a quirk, but they are so much more fulfilling. Somewhere out there, maybe even right now, someone else has the exact same heart as you, in the exact same place. They're meant to be your soulmate, and you two are part of the same soul." Inko explained gently.

The little boy lifted his head some, his eyes sparkling with awe and happiness despite the dull ache in his side. "You mean, someone will like me even though I'm quirkless?" he asked hopefully.

Inko bit her lip slightly, she knew that it was unlikely for soulmates to dislike each other, but the world had changed after quirks became more common. It was still possible for her son's mate to look down on him because of his condition. Still, her heart broke to see her baby so dejected all the time, especially when he was going through so much pain from the mark alone. "That's right, honey…"

"But, then why does it burn all the time?" he asked, his small fingers running over the black mark hesitantly. "Am I doing something wrong?"

"Oh! My dear little Izuku… This is why I wanted to wait until you were older… No, you're not doing anything wrong. Those marks connect you to your other half, and when they're in pain, or scared, or upset you feel it too."

"What about good feelings? Can my soulmate feel that too?" he asked.

Inko pet his hair and nodded, "so try to stay happy okay? Let your other half know things will be okay..."

Midoriya felt tears pool in his eyes. He hated the idea of someone out there hurting like this so consistently; it didn't seem fair. Then he realized how often he got picked on at school and wondered if his soulmate had felt that as well, guilt starting to pool in his stomach. He vowed that he'd find this person eventually, and never let anything upset them ever again.

When Izuku was ten, the only other person he knew to have gotten a soulmate was Bakugo, and the blonde had made sure to rub that in his face. Of course, he hadn't told anyone about his own, fearing what they might say.

When he got home that day, he asked his mother why Kacchan got a mark so much later than he had, and her face saddened once more.

"Something has to happen for two halves of a soul to connect in our world, and that connection is what determines the mark you receive. Do you remember how heartbroken you were when the doctor said you wouldn't ever develop a quirk?"

Midoriya nodded, clutching his side again. "So, I put my mark on him before he gave me mine? We both had our hearts broken and that's why it looks like that?"

Ino nodded and returned to folding clothes. "But, even if it wasn't something wonderful that connected you two, it's something that you can share with your soulmate." She encouraged, lifting his spirits slightly.

Izuku went off to his room and stared at the blackened skin in the mirror, tracing the small white crack with his finger. He wondered if they could fix each other, and if they did, would make the heart whole again?

When Izuku was fourteen, he had his heart crushed again, this time by his idle, All Might. "Damnit… don't cry…" he whispered to himself, "your soulmate will hurt longer if you don't just get over it."

Between Kacchan telling him to jump off a roof and All Might telling him to pursue a different dream, he wondered how badly he was hurting his other half, but he couldn't help it. After years of being told how useless he was, a small, dark seed had begun to grow in his mind.

'What if I never find them…What if I do and mom was wrong and they won't want a quirkless deku like me?'

He shook his head to try and clear it of such depressing thoughts, realizing he'd walked to where another battle was raging. "Did I come here subconsciously?" he mumbled, telling himself he should probably just leave until he realized who was stuck in the slime monster, and he began running towards it.

When Izuku was fifteen, he nervously performed the tests Mr. Aizawa had forced them to do, determined to not let anything else get him down from then on. He had an amazing quirk, his idle as his mentor, and one day, he'd find his soulmate and never let them hurt again.

His eyes scanned the class after Mr. Aizawa had released them from their quirk assessments, breathing easier now that he knew he wouldn't be expelled on his first day. He wondered if any of these students were secretly his soulmate, but doubted it, he was still a teenager after all.

As Midoriya turned and headed away with the rest of the boys to change back into their regular clothes, however, he felt an odd sensation, like someone was looking at him. Sure enough, when he peered around, mismatched eyes were glaring at him coldly, their sharp gaze basically saying that he wasn't meant to be there anymore as someone who'd finished in last place.

Izuku squeaked and turned back around, walking more quickly to the dressing room. He didn't think he'd ever get along with someone who looked at people like that. It was different from Bakugo's angry glares and loud threats. This was a cold intimidation that he truly didn't think he could handle much more of.

When Shoto was four, his quirk manifested, and he thought that would be the end of his already unhappy life. His father, Endeavor, trained him mercilessly, beating him down and trying to break him so that he could be rebuilt in a specific way.

But Todoroki was a kind child and didn't want to be mean to anyone. He wanted to play with his siblings and sit in his mother's lap for hours while she showed him how to make snow instead of just ice.

It was also at four, when Shoto's soul mark appeared, angrily bleeding into his left ribcage and aching for hours. He remembered smiling soon after though, when his mother explained to him that it meant he'd always be loved by her, and someone else too. All he had to do was be patient and find them.

When Shoto was five, his mother poured boiling water on his left side, burning the skin around his eye as he wailed on the floor. He couldn't believe that his sweet, caring mother would do such a thing to him. He'd heard what she'd said when he was eavesdropping at the door, that his left side was unbearable…

Todoroki felt his heart break when those words and her actions finally settled inside his small mind. He said it was his father's fault, but he blamed himself too. How could she hurt him if he hadn't done something wrong?

He swore then that he wouldn't use his fire quirk anymore and tried to scrub his soul mark away. The dark, cracked heart reminded him of his mom's words, 'someone besides me will always love you'.

"Ha! You loved me so much you burned me with scalding water. Soulmates are a lie… and mine's a crybaby too. This stupid mark burns almost every day." He thought bitterly.

Todoroki remembered that they shared pain, but no longer cared to think about what must be causing his other half to hurt so much, nor did he care how he was affecting the boy or girl whenever he'd get beaten for refusing to use his left side.

To him, if he was forced to suffer and deal with it, then his soulmate would just have to learn to cope too.

When Shoto was ten, no one else he knew had gotten a soul mark, and as his was easily covered by his shirt, he made no effort to tell anyone that he had. The girls in his private school swooned over the idea of potentially getting one someday and wondered what it could be.

They were just getting to the age where they started to really notice those of the opposite, and occasionally, same sex. Even though their affections were innocent and childish, it made Todoroki want to freeze the entire school.

He heard them talk about the newest tween romance novel that had come out. Apparently, some people could develop a mark, but their soulmate never did. Other times, soulmates never met and thus had to go through life always wondering. But even worse still, were those who met their fated love and were star-crossed lovers, unable to spend their life together in happiness.

Todoroki rolled his eyes at that, snorting quietly about why they should care. But he didn't say a word, he never did to anybody.

When Todoroki was fourteen, the mark on his skin burned almost as bad as it had the very first time it appeared, the crack seeming to widen ever so slightly as he grit his teeth against the sensation. Despite how stupid he thought the whole thing was, he decided Google why it had altered after so long.

Apparently, soul marks could change in unison if at least one of the two people experienced something strong enough to alter it. In this case, he figured his other half had received some pretty shitty news, seeing as it looked like the heart would finally shatter in two after all these years.

He had no idea what had caused their bond to start in the first place, obviously something bad for it to have appeared as it did, but this was something else entirely. He almost wanted to meet the person to ask… Almost…

When Shoto was fifteen, he came face to face with the dorkiest, most awkwardly happy person that he'd ever met. The boy was small, with a wobbly grin and messy green hair, and he blundered on almost all of the quirk assessments they were forced to do for Mr. Aizawa.

He kept his face stoic, but wasn't really surprised when the teen finished last, he seemed to be nothing but a waste of space in the hero course, even if he had been able to throw a ball really far. That crazy strength meant nothing if the backlash was broken bones and becoming a liability during fights.

When he heard Aizawa say that it was a 'logical deception' and that none of them were actually leaving the class, he almost let his eye twitch in annoyance, especially when he saw the teen sigh in relief and start tearing up. "Crybaby…"

There was something strange about him though, so he watched Midoriya as they walked back to the locker room. Giving a deep glare when the boy caught him staring. He wouldn't be intimidated or made to feel uncomfortable by someone like him.

A triumphant smirk tugged at the corner of his lips when Izuku squeaked and scurried away like a frightened rabbit. At the same time though, his chest pulsed in what he didn't realize was guilt, making him absentmindedly rub his side.

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Okay… Tell me what you think so far!