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Izuku had always known his tendency to mutter thoughts out loud was going to get him killed one day. He'd even known that more likely than not, it would be Kacchan who did it.
He just never expected it to be so embarrassing.
It’s September and it’s still sweltering. They're all grabbing their costumes when he hears Kirishima talking to Katsuki.
"Guess it's gonna be a while before you have to bust out the winter outfit, huh?"
And Izuku, who is a moron, mutters to himself, fairly audibly, "Oh, good." And, because he's a moron and God hates him, pretty much everyone hears.
The entire class turns to look at him. Aizawa sighs and retreats into his sleeping bag, leaving Izuku to face the consequences of his actions— namely, the cocky grin on Kacchan's face.
"What was that, Deku?"
Izuku turns a shade of red that probably does not bode well for his blood pressure. "I-I didn't say anything."
"You said good, didn't you?" Kaminari says. Maybe if Izuku attacks him at full strength he'll use too much electricity and won't be able to talk anymore. "What's that mean? You prefer his summer uniform?"
Izuku locks eyes with Shinsou. He shoots him a look that he hopes says something like can you brainwash me so I am no longer aware of my physical form or the concept of shame , and Shinsou gives him a look back that he's almost certain means no . He looks at Ochaco next, but he knows he won't find help there, because Ochaco had said that if she had to listen to him moon over Katsuki any more, she was going to tell him herself. And Izuku knows that she wouldn't, actually, because she is his best friend and she keeps his secrets, but he also doesn't want to push her.
After that, his eyes find Kacchan’s. That's a bad idea. Katsuki smirks and says, "Why d’you like this uniform better?"
And here's the thing— Izuku could come up with an acceptable reason. He could come up with a handful. Anything from how he knew Kacchan hated the cold, so he preferred knowing he was comfortable, to any sort of rambling bullshit about power output or something that will make everyone tune him out— except at that moment Katsuki crosses his arms, and even in the school uniform Izuku can see the outline of his muscles, his incredibly big, incredibly strong muscles. And Izuku's very dumb, very gay brain latches onto them, and Izuku's very dumb, very loud mouth opens and says, “Arms."
Everyone stops and stares. Kacchan's grin is wicked and sharp enough to cut yourself on. Izuku fantasizes briefly about dying on the spot before he says, "I-I mean! Um!"
He's got nothing. He grabs his hero uniform and flees from the room, vaulting over a desk, green lightning under his skin as he hightails it out of there as fast as physically possible.
In the classroom, Ochaco drops her head into her hands and shakes it. Mina exhales heavily. "Just what Bakugou needed. A boost to his ego."
"You," Ochaco says, when she finds him sulking under a tree when class is done, "are the biggest disaster I've ever met."
“Tell me something I don't know," he mutters, as she and Todoroki sit down on either side of him.
"What are you doing out here?" Todoroki asks.
"Trying to turn into a plant so I don't have to experience human emotion anymore."
Ochaco snorts. "You're so dramatic."
"Besides, plants still feel emotion," Todoroki says unhelpfully. "Right? Like, they're alive. And they like music."
"That is so incredibly not important," Ochaco says, bringing them back on topic with practiced efficiency. "Look, Deku, it's not that big of a deal! Embarrassing, but everyone will move past it as soon as someone else in class does something stupid."
"And it doesn't have to mean anything," Todoroki says, actually helpful this time. "I mean, Bakugou does have nice arms."
"Objectively," Ochaco says. "Shouto’s right. Just blame it on your gay little head and say you have a weakness for arms."
"But I don't, " he says, rather pathetically "I have a weakness for Kacchan!"
Ochaco shakes her head. "One of these days I'm going to send you floating away," she mutters.
"We know that,” Todoroki steps in. "But unless you want the whole class to know that, you should probably just play it off as you having a thing for arms."
Izuku sighs. "I hate everything," he says, because he knows they're right. It isn't even so much because of what the rest of the class thinks— he just doesn't want to make things weird with Kacchan. They're friends now, and Izuku doesn't want to lose that.
It’s just… well, it's not his fault Kacchan had sprouted up to a full two heads taller than Izuku, and his arms had to be incredibly strong to boost him as he flew around. Izuku has remained short and lean, muscles more wiry and evenly spread, with the possible exception of his thighs, which won't stop rubbing holes in the fabric of his uniform. That had certainly been an awkward conversation to have with Hatsume.
Listen, Izuku was the future number one hero and symbol of peace and he was All Might’s successor and he'd already accomplished more before he finished high school than some heroes do in their entire lives— but he's also eighteen and very gay and very, very horny, and sometimes he gets distracted by the sight of his oldest friends arms or chest or the outline of his dick in his pyjama pants when Izuku stays in his room until late, arguing and fighting and watching old All Might videos—
He was getting distracted. It was almost impressive how his brain was always able to make connections that ultimately ended with Izuku thinking about Kacchan’s dick again.
God, what was wrong with him?
"Oi," a deep voice says, and Izuku jumps like a foot in the air and looks around wildly, stopping when he sees Ochaco laughing and Shouto's stone faced expression.
"You two are the worst," he says.
"You have to be sharper," Ochaco says. "It’s more like…" She takes a breath and then goes, "Oiy!"
Even Izuku has to laugh at that. Shouto creates fire in his palm and then says, “ Oiy! " in such an uncanny way that Izuku almost wants to kiss him for a moment.
By the time they get back to the dorms, he's feeling much better, a chorus of oiys and his friends' laughter ringing in his ears.
It isn't that bad, all things concerned. Katsuki keeps giving him these really smug looks, but Katsuki has been giving Izuku smug looks for years, it's just that usually it was because Katsuki had kicked his ass in a fight and not because he knew Izuku was drooling over his arms. When they sit down for dinner Sero calls his name, and when Izuku looks over, Sero pushes one of Katsuki's sleeves up to show off his arm. Sero gets a smack on the head for that, but Katsuki still shoots Izuku a self satisfied smirk, making him turn bright red.
"I think he likes having your attention," Ochaco says into his ear. Izuku looks away from where he was fantasizing about being the pair of chopsticks held in Kacchan's giant hand.
"Don't be ridiculous," he says, because she does this sometimes, gets his hopes up, makes him think things that mean nothing might mean something instead. It just hurts too much. Most of the time, he's able to convince himself that he is happy just being friends and rivals with Katsuki. He didn't even think they'd ever get that far.
But sometimes it’s impossible not to want more.
"Hello? Earth to Midoriya?"
Izuku looks up to where Ashido had apparently been talking to him.
"S-sorry, what was that?"
Ashido puts her hands on her hips. "Seriously? Were you thinking about Baku's arms again?"
Izuku thinks his head down on his desk.
Two days after he ran his big dumb mouth, he cracks and takes Todoroki’s advice. Kaminari makes a comment— he and Sero had by far been the worst— about his "precious Kacchan," and Izuku knew he had to do something before Katsuki found out that Izuku was in love with him and everything got awkward and ruined.
"It’s not like that!" He whines. "I just… like arms."
Surprisingly, everyone accepts that explanation, probably because, as Ochaco had said, Kacchan had objectively nice arms.
And that should be that. It should be done, over. A few days later Mineta falls asleep in class and wakes up shouting "daddy" and everyone forgets about what Izuku had said. Everything should be back to normal.
Except it's not.
Izuku can't quite put a finger on what's different, but when he tries to explain it to his friends, he says that it feels like Kacchan is holding him at arm's length. They're still sparring, still training together, still eating lunch occasionally, and Kacchan even looks over his English homework sometimes. But it's different. Things are missing. Things Izuku hadn't even noticed until they were gone. Things like grins that were softer than any smile he's ever seen on Kacchan's face, or the way he'd yank on Izuku's hair or poke the freckles on his cheeks, or the warm press of his thigh when they sat next to each other. All of that is missing now. No more soft grins or easy touches. Kacchan barely sits next to him at all, actually.
Izuku is miserable. Something is wrong with Katsuki, but he doesn't know what, and he can't just ask. But Izuku has been watching Katsuki for years and he's fairly certain that other than his parents, he knows Katsuki better than anyone. Surely, if there was something wrong with Kacchan, Izuku would be able to figure it out.
The first thing he does is go back and figure out when the change happened, which leads him to the day he had said that he was into arms, not Kacchan.
Next is to identify exactly what the change was, which in this case is all those small things that amounted to Kacchan pushing him away and holding him at arm's length. Izuku considers these things, tries to connect them. It’s easy enough to find a reason why what he said may have set Katsuki off. Izuku had pretty much said that he didn't care that they were Kacchan’s arms. Of course Katsuki's ego had been bruised.
But why react by pushing Izuku away? Izuku had bruised Kacchan's ego before in the past— with how big it was, it was impossible not to bump into it on occasion. But normally, Katsuki would just stomp around for a few days before things settled down. He's never done something like this before.
Look, Izuku is a smart person. Some might even call him a nerd. So he sees these facts laid out— Izuku had explicitly made it clear he wasn't interested in Kacchan, Kacchan had pulled away from him, Kacchan was upset that Izuku apparently liked arms and not just his — he sees these facts laid out and he knows what they should mean, but he can't seem to make that make sense in his mind. Why would Kacchan be upset that Izuku wasn't attracted to him, unless he... wanted Izuku to be attracted to him? But why would he be upset unless he—
Unless he also—
He calls Ochaco.
"Why are you calling me? I'm just downstairs."
"Why do you think Kacchan likes me back?" He says all at once. Ochaco sighs.
"Hang on, I'm coming up."
He's so lucky to have her.
A few moments later, there's a knock on his door. She must have run up here—
He opens the door, and it's—"Kacchan!" He yelps. Katsuki's hands are shoved in his pockets, and he rocks back on his heels the way he does when he's nervous. He nods.
"Can I come in, nerd?"
Izuku stands aside and slides his phone out of his pocket, praying Ochaco checks her messages before she comes up. abort abort kacchan is here if you dont hear from me ive prob been murdered.
He pockets his phone again and closes his door, locking it on the off chance that Ochaco just barged in. She never had before, but with his luck the first time would be when Kacchan was in his room late at night.
Well, okay, it was barely 7pm, but that was late for Katsuki.
"Is everything okay, Kacchan?"
Katsuki scowls and rubs the back of his head. It's unnerving to see him so nervous. "Yeah, s'fine. Just wanted to… talk to you about something."
"Oh.” This was probably a sign, or something. "Um, I wanted to talk to you too, actually!"
Katsuki nods jerkily. Izuku's phone is vibrating in his pocket, but he ignores it. "I," Kacchan starts. "You — ugh." He's clearly frustrated. He tries again. "The thing with you and my-my uniform, you—"
"It's not just arms!" Izuku shouts out before he can stop himself. He slaps his hands over his mouth, but it's too late. Katsuki narrows his eyes.
"What?"
Well— plus ultra, as they say.
"It's not just arms," he says, speaking quickly, eager to get all the words out so he can stop talking. "If it was, I'd be staring at Shoji all the time. It's not arms, it's Kacchan’s arms."
“What,” Katsuki asks again, voice low and deadly. Izuku looks down at his feet.
"Well, it’s all of Kacchan, actually. Kacchan is, um, strong, and tall, and—" he doesn't notice Katsuki moving until he's suddenly looming over Izuku, a bright glint in his eyes. Izuku has to crane his neck kind of a ridiculous amount.
"Is that what it is, De-ku?" And wow, the way Kacchan says his name like that should be illegal. Katsuki places both hands on the door beside Izuku, and holy shit, his hands are as big as Izuku's fucking head. He leans in slightly, getting closer but still making Izuku tip his head back to look up at him, bearing his throat. One of Kacchan's hands could wrap around his neck.
Okay, this is happening. Izuku has never backed down from a challenge, and definitely never one from Katsuki. He stands up on his tiptoes, bringing his face closer to Kacchan's, tilting his head back more and looking up at him through his lashes. "Yes," he says, pitching his voice low. He's never tried to be sexy before, so he's not sure if it's working, but Kacchan's blown out pupils and wet lips are making him feel powerful in the most addictive way. "Kacchan is so strong," he says breathily, knowing how much Katsuki liked being told how amazing he was. "And big, too," Izuku says. It should be a ridiculous line, but Katsuki’s eyes darken and he moves in closer.
"Fucking hell, Deku," he says shakily, and any power Kacchan had has been firmly given to Izuku now. Katsuki’s eyes are glued to Izuku's lips and he's bending down into Izuku’s space like he's being magnetically drawn in. Izuku feels incredibly powerful. "Can I kiss you?"
Izuku grabs him and drags him down.
Katsuki grabs him and lifts him up .
"Oh my god," he says, scrabbling at Kacchan's broad shoulders, legs squeezing around his waist as big hands grip his ass. "Kacchan’s so strong!" Katsuki kisses him again, lips crashing down on Izuku's in a kiss that feels a bit like a fight. His fingers dig into the plush skin of Izuku’s ass, a rumble of deep satisfaction coming up from deep within Kacchan's chest. His mouth is open beneath Izuku's, tongue in his mouth, teeth nipping at Izuku's lip.
"Kacchan— Kacchan bed."
Another satisfied grunt comes from Kacchan as he easily moves Izuku away from the door, supporting his whole weight as he carries Izuku to the bed, which eases any concern that he's going too fast. Technically, if he thinks about it, this has been fifteen years in the making.
Katsuki pushes him down into the mattress, and Izuku is completely dwarfed by his body. He twines his arms around Kacchan’s neck as he is thoroughly and deeply kissed, legs forced wide to accommodate Katsuki's body between them.
Kacchan pulls away, voice rough and the sexiest thing Izuku has ever heard. "Why the fuck won't your pocket stop vibrating."
"Maybe I'm just happy to see you," Izuku giggles, which gets him a bite on the jaw. "It’s Ochaco," he says, as the bites turn into open mouthed kisses and broad licks from Katsuki's tongue. Feeling bold, Izuku says, "If it's bothering you that much you can take them off."
Katsuki's lips go still on his neck. "Deku," he says, a warning in his voice.
"O-or you don't have to!" Izuku quickly backtracks. "We don't have to do anything if you don't—”
"That’s not the problem," Katsuki says roughly. "Want to do fucking everything to you, Izuku."
Izuku can't stop the moan that spills out of him at the sound of his name, and that seems to set Katsuki aflame; he all but tears Izuku's pants off and throws them, and he hears a thump as his phone falls to the ground. Katsuki yanks Izuku's shirt off next before making quick work of his own, and Izuku lets his hands wander gratefully over the expanse of bare skin, mapping shoulder blades and impressive back muscles, nails digging into his biceps. Katsuki also has wandering hands, although he seems mostly preoccupied with Izuku's ass, groping and squeezing, slipping beneath the band of his underwear for skin on skin. He brings their lips back together, groaning into Izuku's mouth as he rakes his nails down Kacchan's back.
"Kacchan's strong," he mutters, near delirious, drunk on each kiss. "So strong, Kacchan, so big—"
"Jesus fuck, Deku," he says, as Izuku brings his hands down to yank at the waistband of Katsuki's sweatpants. He gets the message quickly, pulling back briefly to shuck them off before leaning back in. His hand goes back to Izuku’s ass and shifts him, angling his hips more, and Izuku can't stop the strangled gasp that escapes him as their cocks drag together. "Shit," Katsuki says into his mouth. "You're so fucking hot, Deku, shit."
"You talk a lot more than I thought you would," Izuku says absentmindedly.
"You think about this a lot, nerd?" He can tell that Kacchan is trying to sound nonchalant, but there's an undercurrent to his voice that gives away how much he cares about the answer.
"Yeah," he says. "Yeah, Kacchan, I think about it all the time."
"Tell me," Kacchan gasps in his ear, grinding down against him. Izuku plants his feet on the mattress and ruts up.
"Your arms,” he says, hands travelling to trace over his biceps. "A-and your hands." The word devolves into a moan as one of those hands in question threads through Izuku's hair and tilts his head back more. Izuku is pretty sure he's going to have a hickey. That's a problem for future Izuku. "Thought about your hands on my—my dick and around my throat—"
" Shit ," Katsuki says breathlessly.
"Kacchan, can I— can I touch you?"
"Yeah, anything."
Izuku immediately shoves his hand in Katsuki's underwear; his cock is hard and big, and Katsuki lets out the most delicious noise as Izuku wraps his hand around it. "So big, Kacchan," he moans. "Gonna break me apart."
"What the fuck, Deku, when did you learn to talk like this?"
"I've known you for fifteen years, Kacchan, you don't think I picked up a few things?"
Kacchan lets out another groan. "You're gonna kill me."
Izuku feels so fucking powerful. He strokes Katsuki’s dick, hot and thick in his hand. Izuku has no idea how that’s going to fit inside him, but he's certainly planning to find out.
Katsuki yanks Izuku's underwear down around his thighs and then wraps one of his hands around Izuku's cock, completely engulfing it. It feels so much better than when he does it himself, but Kacchan doesn't keep it there for long. He pulls Izuku's hand out of his underwear and pins it to the bed before he leans back in to kiss him, covering him bodily as he grinds down against Izuku, and Izuku might feel embarrassed at how small his cock feels against Katsuki's, except Katsuki doesn't seem to mind. He kisses Izuku desperately and holds him like he's afraid Izuku is going to disappear if he lets go, and the whole time Kacchan is muttering, roles switched as he babbles and Izuku listens, heart clenching at each whispered praise and curse.
"So good, Deku, fucking perfect, shit, so fucking good for me." The bed, which is probably barely enough to support Katsuki on a good day, is creaking and complaining quite loudly over their combined weight and the steady way Katsuki thrusts his hips against Izuku's. That, much like the hickey, is a problem for future Izuku.
Izuku's orgasm hits him like a freight train out of fucking nowhere. He comes between their bodies, Katsuki's name falling from his lips, loud enough that the whole dorm probably hears. Future Izuku is going to have a lot of problems.
Kacchan comes after him, a guttural "Izuku," punched out of him. Izuku clings to him as they try to catch their breaths, chests heaving against each other. Katsuki tips them over onto their sides, pulling Izuku against him, and he doesn’t even care that their stomachs are both smeared with cum.
In the quiet that follows, Izuku becomes aware of a low pitched vibrating noise.
“I’m going to blow your phone up,” Katsuki growls. “Fuckin’ literally.”
“Sorry, sorry. I’ll put it on silent.” He squirms out of Kacchan’s arms and leans his torso off the bed, fumbling for his pants. A big, strong arm wraps around him to keep him on the bed, and Izuku feels so light he thinks he might float away.
He fishes his phone out of his pocket and Katsuki hauls him back onto the bed. He has a lot of unread texts from Ochaco.
UO: wait wdym he’s there
UO: deku pls i need answers
UO: WHATS HAPPENING
UO: what was that thump. was it your lifeless body hitting the floor bc bakugou killed you
UO: rip deku. he died as he lived, pissing off bakugou katsuki
UO: okay seriously what’s happening
UO: deku wtf is that creaking
UO: midoriya izuku are you having sex at 730 on a tuesday???
UO: WE CAN ALL HEAR YOU???
UO: you haven’t even gone on a date yet
MI: don’t slutshame me
UO: DEKU OH MY GOD???
Kacchan makes an annoyed grumble, unhappy that Izuku’s attention is elsewhere.
MI: i’ll give you the details later bye
UO: deku no!!!!!!! Now!!!!
He turns his phone on silent and puts it on his side table, and Kacchan immediately spoons around him; once again, Izuku is completely dwarfed by him. It’s a feeling he could definitely get used to. Katsuki shoves his nose into the nape of Izuku’s neck, pulling him in closer when he shivers. He grabs the blanket with one hand and drags it over them both.
“I am not going to sleep,” Izuku says firmly. “It is 7:30.”
“M’tired.”
“It’s 7:30,” he says again. Katsuki just nuzzles in closer, which is adorable and unexpected and Izuku is absolutely weak to it. “Fine,” he concedes. “But the minute you start to snore I’m going downstairs.”
“I don’t snore,” Katsuki mumbles.
“Yes you do,” Izuku says. “I have years worth of evidence from sleepovers.”
“Nope,” Kacchan says. “Wasn’t me.”
Izuku giggles. “Whatever you say, Kacchan.”
He thinks that’s it, but after a few minutes Katsuki says, “So will you, like… go out with me, then?”
Izuku snorts. “If you sound a little more excited about it, maybe.”
He feels teeth on his ear. “Be my fucking boyfriend, shitty Deku.”
“I always knew you’d be a hopeless romantic, Kacchan.”
“Damn right,” Katsuki says, lips finding Izuku’s skin again. "Is that a yes?"
Izuku turns around so he can kiss him again. "Yes, it's a yes."
Two months later, the winter uniform comes out. Izuku doesn't mind as much this time; now he has access to Kacchan's arms whenever he wants.