Chapter Text
The first time, it just kind of… happens.
It's a normal day. A warm Saturday afternoon, soft sunbeams falling through all the windows and spilling onto the ground like honey. Completely innocuous. Completely innocuous until Katsuki tries to open Izuku's dorm room door, and it doesn't budge. He left a jacket in there yesterday—and okay, maybe his idiot brigade is off doing something stupid somewhere loud, maybe he's a little bored, sue him—so he figured he'd duck in and grab it, but the door's locked. He frowns to himself. Weird. Izuku's door is almost always unlocked when he's home.
Katsuki and Izuku reached the point of dropping in unannounced, barging into each other's rooms without warning, sometime toward the end of second year, and the habit just stuck. Since it's not open, though, it's not like Katsuki has much choice. He bangs his fist against the door.
"I know you're in there, nerd!" he calls.
There's a gasp loud enough to be heard through the door, followed by what Katsuki could swear is a muffled curse—even though Izuku almost never curses, not outside of combat—followed by a muffled thump, like someone falling out of bed, followed by a panicked voice calling, "Uhh, one second!!"
What the hell?
Katsuki stands there for almost a full minute, growing more and more impatient, before Izuku finally opens the door. And he looks—
Well, he kind of looks like shit. Not in too bad a way, necessarily, he's just a little sweaty and his hair is wild and his eyes are wide and his cheeks are flushed. Even his breathing is a bit fast.
Katsuki's eyes narrow. "…You good?"
Izuku nods fast. "Yeah. Yeah! I'm fine. I'm good. I'm great, even! What, uh, what did you need, Kacchan?" His voice is all high and squeaky.
Something's obviously off here, but Katsuki can't put his finger on it. Was he napping? Are the nerd's nightmares getting bad again? It's the right time of year for it.
(Granted, most of the year is the right time of year for it.)
Not wanting to scare Izuku off, Katsuki decides to keep things light. He smirks and leans forward a little. "What, you in here jerkin' off or something?"
He means it as a joke. It's so absurd that it couldn't be anything other than a joke. And he knew exactly how Izuku would respond. He would roll his eyes and groan and shove him and blush and say, Kacchan, you can't just say things like that!
But that's not what happens. Instead, Izuku's whole face goes paper white before turning bright red again so suddenly that Katsuki's almost afraid he's going to pass out on him. Izuku is silent.
Holy shit.
Katsuki's smirk turns into a full-on grin, wide and dangerous. Like a shark that just smelled blood and a kid on Christmas morning all at once. "You're kidding."
Izuku lets out an inhuman little whining noise. It sounds a bit like air being let out of a balloon. "Please drop it," he says, pleading but also resigned. He knows Katsuki too well.
"No way in hell!" Katsuki barks a sharp laugh. (Tries not to imagine Izuku laying in bed with his hand on his cock, fumbling to hide the evidence when he hears a knock at the door. Fails.) He pushes his way into Izuku's room and shuts the door. The brief skin-on-skin contact their arms make feels like fire. He can feel his jeans getting tighter around the crotch. "This is— this is too good, holy shit! It's the middle of the day, you fuckin' perv. What, nothing better to do?"
"Kacchan, of all the things you make fun of me for, can this not be one of them? Please?" He's backed himself against the edge of his desk. It's still a little muffled by his hands, but Katsuki thinks he mumbles something about how he should've stayed on the run.
And Katsuki knows he's probably crossing a line here—several lines, even—knows it's best to leave some things alone, but for some reason, he just can't bring himself to drop it.
(He knows why. It's the same reason he has to adjust his jeans while Izuku's still hiding. It's the same reason he relishes the red in Izuku's face. It's the same reason he showed up here in the first place.)
Katsuki steps closer, slowly approaching like a predator closing in on a hunt. Now that he's paying attention, he can see the bulge in Izuku's shorts. His dick's tucked into the waistband, but with basketball shorts, that's really not contributing much in the hiding department. "You're getting off on this," Katsuki realizes gleefully. It's a statement, not a question. He feels like he's going insane, like he's been possessed by something, like he's not fully in control.
"Kacchan," Izuku begs one more time, finally looking him in the eye. His big, green puppy dog eyes are wet with humiliation. "Please."
But Katsuki's never been especially merciful.
Once he's close enough to feel the embarrassed heat coming off Izuku on waves, he hunches over. His breath ghosts hot over the shell of Izuku's ear. Izuku actually fucking whimpers at that.
Before Katsuki can question what's come over him, before he can stop himself, he whispers, face-splitting grin still firmly in place, "What were you thinking about?"
The tears in Izuku's eyes start to fall. Katsuki chooses to ignore the way his dick throbs at the sight. "This is mean," Izuku gets out through the fat tears rolling down his cheeks. "Even for you."
Katsuki knows that. He knows. And he doesn't want to really be mean to Izuku. But something about this whole situation has flipped a switch inside him, and he just can't help himself.
"You like it when I'm mean," he murmurs, another statement of fact. He tries to soften the blow by pressing his hips gently against the side of Izuku's. A reassurance that this isn't just mindless cruelty, that it's not just about mocking Izuku anymore—as if it ever was—that Katsuki isn't perfectly unaffected the way he plays at being. Izuku tries and fails to repress a shudder at Katsuki's hard dick digging into his hipbone.
"Yeah," he breathes, gazing up at Katsuki with wet, half-lidded eyes, "I do."
Katsuki sucks in a sharp breath. Shit. What the hell is he doing? This is gonna fuck everything up. They just got their friendship back, but there's no coming back from whatever this is. He's about to step back and— He doesn't even know. Apologize? Run away and hope they can pretend this never happened? Blast himself into the sun for listening to his dick one time only to fuck everything up? Whatever. It doesn't matter because before he can do anything, Izuku grabs his wrist firmly and says, quiet and breathy, "Can I?"
And suddenly, Izuku's holding all the power here.
Katsuki doesn't know exactly what Izuku's asking for, but he knows it's a bad idea. He knows he should leave. They should both walk away and try their best to forget this ever happened.
He also knows he's horribly weak for Midoriya Izuku.
Katsuki swallows thickly. Izuku's pupils are blown wide and his full cheeks are still red and sticky with humiliated tears. He looks like sex incarnate. Katsuki doesn't even know what he's agreeing to, but he nods anyway.
Izuku spins them and falls hard to his knees, and all rational thought falls out of Katsuki's head along with him. Scarred fingers make quick work of the button and zipper on Katsuki's jeans, hooking into the waistband and pulling down hard and fast, just enough to expose the clothed bulge underneath, like he's afraid Katsuki will change his mind.
Katsuki wishes he was really that strong.
It's only when he feels himself twitching at Izuku's damp breath seeping through his boxers and warming the sensitive skin of his cockhead that he remembers—
He doesn't do this. Like, almost at all. For all his bravado and teasing, Katsuki is woefully unprepared for this. He's always had a pretty low libido, and that's worked out very well for him. Not like he has time for that shit anyway. Between school and training and having a social life forcibly thrust upon him, he's busy as hell. He's always thought the fact that people do such stupid stuff because of sex is ridiculous. It all sounds like so much work, and for what? Like, sure, Izuku's hot, but Katsuki has at least some self control. If he didn't, the whole feelings thing would've gotten out ages ago. He is perfectly happy jerking off a few times a month, pointedly ignoring whatever images his brain conjures in those moments and any guilt they may or may not bring, and getting on with his life.
That being said—looking on reverently like this at Izuku on his knees for him, seeing those pretty pink lips plant light kisses along the tent in his boxers like they're afraid he'll fall apart—Katsuki thinks he might get it now.
"Shit, Izuku," he hisses, threading a hand into Izuku's hair. It's soft, and he's hoping the feeling will help ground him.
Izuku keeps nosing along the outline of his clothed cock, mouthing at the fabric of his boxers. There's already a little wet spot forming at the front that has nothing (or everything, depending on how you look at it) to do with Izuku's saliva—embarrassing, Christ—and when Izuku licks at it, it feels like every muscle in Katsuki's body tenses at once.
Izuku takes this opportunity to tuck his face into the spot where Katsuki's thigh meets his torso and fucking giggle. As if he's got any right to be all adorable right now.
"Kacchan's so sensitive," he mumbles. "It's cute."
"What the fuck?" Katsuki exclaims. "I am not fucking cute!"
"Okay, Kacchan," Izuku concedes, clearly only for Katsuki's benefit. He's still smiling. Bastard.
Katsuki is about to keep arguing, but the next thing he knows, Izuku's pulling down his boxers, and he can't quite remember what he was so mad about.
Izuku spends a moment just… looking. It's fucking unnerving. Then, he gently pulls back Katsuki's foreskin—and Katsuki does not gasp or have any sort of noticeable reaction, fuck you fuck you fuck you—and looks some more.
"Pretty, Kacchan," he says, wonder in his big, green eyes.
"Shut the fuck up," Katsuki hisses. He has a high tolerance for many things; embarrassment is not one of them.
And right then, Izuku grabs him at the base and licks a fat stripe up the underside, making a point to nudge at the spot right under the head.
Katsuki sees stars. There is no overstating how different this is from his own hand. Holy fuck. He gasps and makes an aborted sort of moaning, grunting sound that he didn't know he could produce. The hand not in Izuku's hair flies back to help him brace himself on the desk. "Fuck, Izuku!"
Izuku just starts stroking in response.
Katsuki's eyes keep trying to close, but he can't bring himself to shut them. On the other hand, he'd really like this to last more than 30 seconds and that's just not feasible if he's looking at this beautiful boy on his knees for him. He compromises by looking around the room and—
Jesus fucking Christ.
Katsuki forgot where he was for a second. Thank god Izuku's diversified his merch collection over the years because if there were 50 different versions of just All Might staring Katsuki down right now, he thinks he might die again. Still, the countless inanimate versions of his mentors, friends, and future coworkers are haunting. If Izuku weren't actively lapping at his cock like a melting popsicle, Katsuki would be out of here at light speed.
Fuck this. Premature ejaculation or not, Katsuki turns his gaze back to Izuku. We, he thinks to himself, are never doing this in his room again.
Every stroke of Izuku's tongue shoots down his spine like lightning—
Wait. Again?
Are… are they doing this again? Is that what this is now?
Just before Katsuki can start spiraling about ruining the most important relationship he has in life, Izuku takes the head of his cock into his mouth and tongues at the weeping slit there. Katsuki's hips shoot forward before he can stop them, but Izuku's reaction time stays intact even when mid-blowjob, apparently. He grabs Katsuki firmly by the hips and holds him to the desk and Katsuki's dick is still in his mouth and that display of strength is maybe the hottest thing that's ever happened to anyone in history.
"I-Izuku, I'm—" His warning is cut off with a groan as Izuku twists his tongue and sucks just right to make Katsuki implode and he comes right then and there.
"Fuck—!" he exclaims. Katsuki's whole body tenses and Izuku's still holding him to the desk and Izuku's not pulling away and everything shoots straight into his mouth and he seems perfectly unbothered. The opposite of bothered, even. He hums contentedly around Katsuki's sensitive cock, and the vibrations make him hiss.
"Shit, Izuku," Katsuki says, panting. Jesus Christ. Is that what sex always feels like? Maybe he has been missing out.
Izuku finally lets the cock fall from his mouth, carefully tucks it back into Katsuki's boxers, looks Katsuki dead in the eye, and swallows.
Holy fuck.
Where the fuck does this nerd get off being the sexiest guy alive? Where did he learn to do that? He's a loser virgin; he needs to start acting like it.
Katsuki just shudders. If it had been any more than maybe 30 seconds since he'd come, he would be rock hard again.
Izuku looks absolutely debauched, face red, lips even redder and shiny and wet, hair mussed and sweaty. He's looking up at Katsuki like he's the only thing in the whole world.
Meanwhile, all Katsuki can look at is the big, dark spot on the front of Izuku's shorts. He must be absolutely dying here; he's been hard for a while, especially considering whatever time he spent horny before Katsuki got here.
"What do you want?" Katsuki asks. He hopes it comes out in an I want to get you off way instead of his usual what the fuck are you looking at? way.
Izuku just glances away and whines a little.
Katsuki raises an eyebrow. "So, I'm free to go, then?" he teases, smirking.
"No!" Izuku exclaims, panicked. "It's just… embarrassing."
"Everything you do is embarrassing, nerd."
Then, Izuku asks, all shy and sweet, "…Can you. Finger me? Please?"
Jesus fucking Christ. Katsuki's gonna hear that playing in his head every day for the rest of his life.
"Shit, Izuku. Yeah. Yeah, I can— Fuck."
Izuku stands—his knees must be killing him, Katsuki thinks deliriously—hooks a finger into one of Katsuki's belt loops, and pulls him over to the bed.
The bed where Izuku was laying down and fucking into his own hand earlier. Katsuki might not survive.
A little nervously but mostly like it's nothing, Izuku shucks his shorts off—not his underwear because he wasn't wearing any, fuck—sits down, and reaches under his pillow. His hand comes back out holding a mostly full bottle of lube.
Someone makes a helpless sort of groaning noise, and it must be Katsuki because Izuku's eyes darken not insignificantly.
"Under the goddamn pillow?" he asks incredulously.
Izuku flushes even more, which Katsuki didn't really think was possible. "Well, if you'll remember, you kind of interrupted something earlier."
As if Katsuki could forget.
He scoffs and rolls his eyes. "Yeah, yeah. You poor thing."
Izuku's eyes widen a little and he looks away quickly. His breathing is heavy. Hm. They'll be exploring whatever that was later.
For now, Izuku is laying back and handing him the lube like it's something precious, and he supposes it kind of is. Or, at least, what he's going to use it for is.
Izuku all spread out like this is a fucking wet dream come to life. Face bright red, cock the same color—not to mention fucking freckled—and leaking onto his T-shirt, hands gripping the sheets like his life depends on it. He's absolutely breathtaking.
Katsuki's trance is semi-broken by Izuku lifting his hips and sliding a pillow underneath. The motion makes his cock bob, leaving a dark, wet dot on his stomach where it meets the fabric of his shirt. Katsuki's overwhelmed by the sudden urge to lick over every single inch of him.
Instead of eating Izuku alive, Katsuki just raises an eyebrow. "You sure seem like you know what you're doing here."
Izuku glances off to the side. "Maybe a little."
Katsuki's covered his fingers in lube and is circling Izuku's hole with one of them—thank you, embarrassing second year sex ed and even more embarrassing late-night internet searches for his cursory sex knowledge—when Izuku starts squirming and huffs.
"You can— you can, uh, start with two."
Katsuki is about to give him some shit for telling him what to do, but he's immediately distracted by the fact that when he applies light pressure with his finger, it slips right in.
Holy shit.
"You— Were you— Fuck." Katsuki can't even string a proper sentence together which would probably be embarrassing if he could think about anything except Izuku fingering himself alone in his bedroom.
Izuku's the reddest Katsuki's ever seen him. "I, um. I was… t-trying?"—Katsuki takes Izuku's advice and pushes a second finger in, thrusting slowly—"Uh, I like it, um, a lot, but it's— it's kind of hard with my hand and t-the angle. My joints get all achy and— Okay, I really can't give a concentrated answer right now!"
"That good, huh?" Katsuki asks, smirking.
"Yes," Izuku whines, and his earnestness is usually just endearing but it's somehow become sexy here. "You— Your fingers are longer than mine, and— Ah!"
He cuts off right as Katsuki feels something under his fingertips. Found it.
This is going to be fun.
"You never answered my question," Katsuki says casually as he keeps up his slow thrusting pace, carefully stroking just shy of Izuku's prostate.
"W-what question?"
Katsuki leans down until he's next to Izuku's ear. "What were you thinking about?" he whispers, an echo of how this whole thing started.
"Ah! I, uh—" Izuku gasps sharply as Katsuki scissors his fingers apart "—I don't wanna talk about it."
"Some freak shit, then," Katsuki concludes, mostly joking. He slips in another finger on his next push.
"N-no! Not— not really! It's just… personal."
"Three fingers up your ass ain't enough to get personal?"
Izuku's arms fly to cover his flushed face. "Kacchan!"
Katsuki laughs. "Okay, not freak shit, then."
What would make Izuku all cagey like this…? A horrible, horrible thought hits Katsuki.
"Was it," he starts, wetting his lips, "someone? Someone we know?" He pulls Izuku's arms away with his free hand. "And don't hide from me."
Izuku squeaks. Not a pleasure squeak, but a panic squeak. Bullseye. Katsuki's not sure he's ever been so upset about being right before. Something molten and possessive begins roiling in his gut. "Who." He can't bring himself to ask it like a question.
Izuku's arms twitch like he almost covered his face again but thought better of it. Good boy.
(…Add that to the list of thoughts Katsuki's had this afternoon that he doesn't have time to unpack right now.)
"No one! Or— someone, I guess, but not like— Uh." Izuku's gone full deer-in-headlights mode. Katsuki feels like he's won and lost the lottery all at the same time.
He runs through his mental list of their classmates, looking for likely suspects. "Round Face?" She and Izuku dated—if you could even call it that—for about two weeks at the beginning of second year before going back to being friends. It was painfully awkward to watch, but who knows.
Luckily, Izuku actually laughs at the suggestion, even with Katsuki inside of him. "No! No, no, god no. Ugh, don't talk about Ochako when we're l-like this. Unless you need a boner killer for some reason."
Holy shit. First of all, Katsuki's going to think about how Izuku's little golden-boy voice sounds saying boner every day for the rest of his life.
Second of all, apparently he needed that, because in whatever's left of his brain, the part that hasn't been consumed by hunger and heat and IzukuIzukuIzuku, some lingering insecurity he didn't even know he still had fades away.
Next on the list, as loathe as he is to admit it, is… "IcyHot?" he grits out through his teeth.
Izuku groans. "No, ew. Can you stop guessing? You're not gonna get it, just— No, it's not… any of my other friends, okay? T-trust me."
In an amazing show of strength and personal growth, Katsuki just grumbles a little before letting it go—for now; don't think for a second he's capable of leaving this question unanswered indefinitely—in favor of petting firmly over Izuku's prostate.
Izuku inhales sharply and makes an intoxicating little whimpering noise as entire body spasms, head flying back to hit the pillow with a thud. His hips have started moving in these cute little jerks like he's trying to hold them back but can't. It makes Katsuki want to eat him alive, but he settles for biting at his neck.
"KacchanKacchanKacchan, I'm gonna— I just need— c-can I…?" His strained voice vibrates through Katsuki's lips.
When Katsuki speaks, he can feel his own hot breath reflecting off the thin skin of Izuku's throat. "What?"
Izuku squirms, fueled by something more like nerves or embarrassment than lust this time. "Can— can I t-touch myself? Please?"
…
Katsuki would like to make sure it's on record that this is all Izuku, okay? Completely unprompted, asking Katsuki for permission to touch his own goddamn dick. Politely, for that matter.
"Fuck," Katsuki says, heartfelt. He's stopped moving completely because that's what happens when you feel like you've been punched in the fucking gut with arousal (or anything else, for that matter).
Someone less deranged might've realized from that reaction that they said something absolutely fucking insane, but not Izuku.
Izuku just huffs and squirms some more like Katsuki's the problem here. "Kacchan!" he exclaims, panting. "What the hell!"
"Me? Me, what the hell? You, what the hell! Don't fucking 'Kacchan!' me! You can't just— just say shit like that, holy fuck!" Katsuki stammers. He can feel his ears burning. Embarrassing.
"But I was right there—" Izuku stops cold. A slow smile spreads over his face.
This cannot be good.
"Wait a second… Did you like that?" he asks like he already knows the answer. Smug bastard.
"I don't— I—"
"You so did!" Izuku fucking giggles because, again, smug bastard.
Katsuki feels like he might explode. He pulls his fingers out of Izuku and wipes them on his sheets just to spite him. For a moment, Izuku shudders, but then his eyes sharpen, and he's on top of Katsuki in a split second, arms draped over his shoulders, nose buried in the crook of his neck.
Katsuki's about to ask what the hell he's doing, but Izuku beats him to speaking. "You never answered my question," Izuku says.
"Don't fucking quote me—"
"Can I touch myself?" he asks again. Katsuki can feel his lips just barely brushing his skin when he speaks, and it's driving him wild.
"I-I don't fucking— Whatever! I don't care what you do."
He can feel Izuku smile against his neck. Izuku always has been good at Katsuki-to-Japanese translation.
He, with absolutely no hesitation, reaches into Katsuki's undone jeans again and pulls out his cock. Again.
(And yes, Katsuki's hard again. Duh. No fucking shit. Izuku's a wet dream walking.)
"What the hell are you—?" is all Katsuki can get out before Izuku's gripping both their dicks firmly in one big, scarred hand.
The first thing Katsuki feels is pure, unrelenting heat. The second is wet because Izuku's fucking leaky when he's like this, apparently. The third is the feeling of being maybe the closest a person has ever been to orgasm without tipping over the edge.
It's ridiculous, really, because this should logically be nothing compared to earlier, but something about the way Izuku's panting so that Katsuki can feel his breath and the way Izuku's straddling him and the way Izuku's wrist twists just so is fucking killing him.
"Izuku, I'm— It's—" he manages.
Izuku nods frantically in agreement. "Yes, Kacchan, please."
And Katsuki doesn't know what Izuku's begging for. It's probably nothing specific, just words falling out of his mouth. But Katsuki does know this:
It's fucking hot.
It's hot, and it has him seeing white, and it sends him flying straight over the edge. He sucks in a sharp breath, tenses, and spills hot and sticky all over their cocks and Izuku's hand.
Izuku whines wordlessly and starts bucking his hips like they're moving on their own.
Just as the stimulation's going from good to bad, Izuku's hips jerk one last time, he lets out this pathetic little whimper, and he comes into his own fist.
Izuku's cum is touching Katsuki's skin right now, and he's not sure he'll ever recover from this.
They sit there for maybe two minutes, catching their breath, before Katsuki becomes acutely aware of how fucking disgusting he feels.
"Izuku."
"Hm?" he hums dreamily.
"Get offa me. We need to shower."
"Oh. Oh! Right!" he exclaims. A little slow on the uptake, but he scrambles off of Katsuki once the words register.
They wipe off in silence and walk to the showers, but it's not uncomfortable. It should be uncomfortable, probably, but it's not.
Katsuki teases Izuku about his hair. Izuku scolds him for it. They argue over who's going to get the higher score on the math exam on Tuesday. (Katsuki, duh.)
Business as usual.
When Katsuki gets back to his room, he slumps against the door as soon as it's closed and slides all the way down until he's sitting on the floor.
What the fuck just happened?