BakuDeku
Being a hero wasn't easy. Villains constantly popping up, rescuing someone from falling debris, and sometimes taking risk that may or may not guaranteed you coming back from it. It was that last bit that had Midoriya Izuku thoughtful.
When he was younger, he always respected All-Might. Not only because he was his favorite hero, but also because the number one hero at the time had risked his life many times fighting and protecting, and that was something Izuku had always wanted to do - on top of having a cool superpower. Having been diagnosed of being Quirkless had hurt, losing his best friend even worst, and then being told by the person he looked up to that he couldn't be a hero without one initially kind of broke his spirit. At that time, he had been ready to give up the dream and resign himself to an average, boring lifestyle - had the green slime monster incident hadn't taken place.
Funny how life works.
It's been a long time since All-Might passed down his quirk onto him, and he made it into the UA. A lot has changed since, especially with the recent soulmates and soul-bonding that were popping up.
The soulmates thing wasn't really new, having been around long before quirks were. There had been stories about how soulmates came to be, ranging anywhere from something obviously fairytale - such as the world bursting into color the moment soulmates met - to something more idealistic, such as a simple spark when you hold hands with your soulmate. Izuku didn't know how any other soulmates met, but he remembers the first time he realized Katsuki was his.
It was the first time they met, back when they were kids and Izuku hadn't known anyone - not when he was just starting to talk anyway. His mother had set up a playdate for him with Katsuki, since her and Katsuki's mom were good friends, and he had been so excited. At the time, Izuku had forgotten Katsuki's name, but still remembered him from his blond hair and red eyes. There had been something about that combination that had little Izuku hook, and he refused to let Katsuki go.
When the doorbell rung, Izuku came running to the door, nearly stumbling.
"K-Kacchan!" He hiccupped, just as the door open and revealed his neighbor, who turned out to be his best friend. In that moment, for Izuku, it was like the world had gotten brighter, happiness swelling inside his heart, and he couldn't stop smiling. Katsuki had been the same, if the smile on his face is anything to go by. Before their quirks appeared, the two of them had been happy, playing with each other and Izuku admiring Katsuki's confidence and knowledge. They both fanboyed over All-Might, and every time Izuku reached out to hold Katsuki's hand, his heart did a funny leap and caused him to tighten his hold on the blond.
That was the moment when the thought I'm never letting you go came to mind. Especially when Katsuki then told Izuku that when they become heroes, they'll be together - as partners. It had made Izuku so happy.
But of course that happy childhood memory was overshadowed by the fact that Katsuki became a prick, and the prickliness only grew more as they've gotten older. The love and admiration Izuku had for Katsuki never wavered, but with it came the fear (because of Katsuki's usage of quirk, intimidating features, and the fact that he may never catch up to Katsuki), the hate (because of the bullying, because Katsuki grew a fat head, because Katsuki never really understood Izuku - the same way Izuku never truly understood Katsuki), and then sadness (of never repairing their relationship, of always being stuck between friend or not friend). It had continued to be that until finally, All-Might pretty much told them to calm the fuck down and told Katsuki his secret. Since then, their relationship how gotten a lot better.
Izuku hadn't been sure if Katsuki knew that he was his soulmate, if he even wanted one, but when Izuku had almost gotten himself killed during his time of being a newly Pro Hero, he'd gotten his answer in a screaming match.
"WHAT THE FUCK, DEKU?! DO YOU HAVE A DEATH WISH OR SOMETHING?!"
"IT'S NOT LIKE THAT, KACCHAN! I COULDN'T LET INNOCENT BYSTANDERS GET HURT!"
"YEAH, AND AS A RESULT, YOU WERE ALMOST KILLED, ASSHOLE!"
"I DON'T UNDERSTAND WHY YOU CARE SO MUCH! WE DON'T EVEN PATROL THE SAME AREA!"
"HAVE YOU EVER THOUGHT THAT MAYBE, JUST MAYBE, I CAN FEEL THE SHIT YOU'RE GOING THROUGH, HAAA?! EVER THOUGHT ABOUT THAT SMARTASS?!"
Katsuki probably hadn't meant to let it slip, especially when their voices were loud enough for other people to hear. And of course the media caught on fast:
GROUND ZERO IS DEKU'S SOULMATE???
It was awkward, to say the least, but about time they actually manage to sit down and talk about it, Izuku realized he may have a chance - one that he was always hoping for. It had been hard to have an actual normal date without something interfering - because even now, the idea of the two leading heroes together is still a shocker for some - but they've managed, and it seemed like they both found themselves falling deeper and deeper in love the more they spent time together. It had gotten to the point where they were now partners, and even had the Wonder Duo nickname stuck to them like glue. Eventually, Katsuki had mentioned wanting to soul-bond.
"You sure? There's always a risk." He asked, a bit concern as he looked at his partner, lover, and soulmate. Katsuki rolled his eyes.
"Deku, I be damned if I let a stupid thing such as soul-bonding take me out after all the shit we've been through. I'm confident we can make it work." Izuku smiled.
"Yeah. You're right."
After soul-bonding, Izuku couldn't help but shiver as he felt Katsuki's emotions wash over him. They were just like the blond himself - explosive, loud, domineering, but Izuku didn't feel suffocated; probably because Izuku's own emotions were just as intense. The two souls clashed, but in the way that felt all too good rather than repulsive. It was almost like having a piece of Katsuki wherever he went, and despite all the loudness, there's a part of Katsuki that is rarely shown, but often felt; his soft, caring, side. The side that Izuku hadn't noticed, but now that he did, he didn't want to let go. It felt tender, small, but there was so much love and affection in that part, it almost brought Izuku down onto his knees and cry.
"Are you done being fucking weird?" A thought came across his mind as he made his way home, tired and bruised.
"It's not weird, Kacchan. I love your soul!"
"That's creepy as fuck to say. Thank god you aren't talking out loud."
"Kacchan! Don't be so mean! I can feel your laughter!"
"When are you coming home?" Katsuki asked, and Izuku could feel him shift inside his mind. He placed a hand on Katsuki's soft, but battered (not as much as his own) one.
"I'm on my way now. Why?"
"No reason." There was a small amount of content wavering through the bonds, and Izuku smiled.
"Katsudon for dinner?"
"And I already have a bubble bath waiting for you. Better thank me you fucking nerd." Katsuki smirked, and Izuku snickered.
"Thanks, Kacchan! I love you!" Izuku had to stop himself from laughing out loud when he could feel Katsuki's embarrassment. Back then, if they had been in UA, Izuku would've thought he'd gotten angry with the way Katsuki bristled over anything nice, but now he knew better.
"Yeah, yeah. Fucking love you too, nerd."
Izuku smiled.