[NSFW] FIC - "Your Hips Fit Mine"

DKBK | canonverse | post-canon | getting together | crack treated seriously | humor

Five times Izuku and Katsuki have crotch to crotch action, from first year to third.

Written for the DKBK Fic Exchange Round 1!

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YOUR HIPS FIT MINE

I.

A few days after Katsuki turned sixteen, he ran into Izuku outside their local manga shop. The nerd was carrying a bag that Katsuki suspected contained the latest chapter of a mecha series he'd spotted Izuku reading last week. He tamped down the reflexive urge to shoulder check him and would have carried on pretending the other boy didn't exist, except then Izuku nervously cleared his throat.

"Hey, Kacchan," he said with forced cheer. He lifted the bag with the manga shop's logo on the side. "D-Did you want to, maybe, um, read this together? It's a pretty cool series about–"

"The fuck are you talking to me for, Deku?" Katsuki snarled, a haze of red surging within him, outrage suffusing his words. "Just because you tricked your way into UA doesn't mean you're my equal. You're still a shitty nerd, and I don't want or need your company. We're not friends, and once the teachers at UA see how useless you are, we won't be classmates either."

Izuku's weak smile wilted entirely, and his brows crashed together. He had the nerve to look upset. Sneering, Katsuki made to shove past him at the same time Izuku darted forward to pass Katsuki.

Normally, Katsuki would've had no trouble avoiding contact. But he blamed blind rage for the way they collided. Izuku had apparently put on a lot of fucking weight lately, because he completely bowled over Katsuki. They went down in a tumble of long limbs and hard shins and a string of curses.

"What the fuck?!" Katsuki screeched when Izuku shifted, all but kneeing him in the crotch.

Katsuki's elbow caught him in the gut, sending him sprawling forward again and landing face first against Katsuki's chest. The rest of him landed heavily between Katsuki's splayed legs. He sputtered, face burning, palms sparking, before Izuku scrambled away and fled, not even bothering to retrieve the bag he'd dropped in the scuffle.

II.

During their first-year internship with Endeavor, they were required to attend specific social events. 'For the corporate experience,' according to Burnin. It'd sounded like pointless pandering to him.

Their first event was a charity ball hosted by the HPSC. They were raising money to fund research for restoring victims of irreversible quirks. While certainly of value, the event topic caused Izuku to glower briefly at his feet, his hands twitching at his sides like he was trying not to clench them. Then, just as quickly, a bright smile replaced the look. No one but Katsuki noticed.

They arrived at the ball dressed in sleek suits and glossy Oxfords, their hero gear tucked away in their suitcases with the Todorokis' chauffeur. It wasn't the first time he'd seen Izuku in formalwear, but the eye-bleeding disaster he'd worn to the Shields' party in America wasn't worth remembering. This time, Izuku had rented a properly fitted suit, courtesy of Endeavor's connections. Katsuki was pretty sure the new Number One just hadn't wanted Izuku to embarrass him with garish yellow suspenders or something.

Anyway, that meant Izuku was dressed in a dark green suit, the jacket stretched snugly over his broad back. He wore a black button-up beneath along with a matching bow tie because the nerd still couldn't knot a tie to save his damned life. He did fill out the suit pants really well, though, Katsuki's gaze continually drawn to the black piping down the pant legs.

It was weird. He never would have thought Izuku could clean up so well. Even his hair had been tamed into something moderately less shameful. Katsuki wanted to tunnel his fingers through the thick curls and muss it up so it'd look more familiar.

They entered the venue through wide glass doors dressed in satin bows and elegant drapes, the heels of their shoes clicking against the tiles. Katsuki frowned at Izuku's back a moment longer, eyeing the way it hugged his waist before looking away.

His gaze met Todoroki's. The other boy raised his white eyebrow.

There was no explanation for the heat that rose in Katsuki's face. He had nothing to be embarrassed about. He just wasn't used to seeing Izuku in something that actually fit him, rather than his usual t-shirts and baggy shorts. Nothing suspicious about that.

Ignoring Half-and-Half, Katsuki stalked ahead, quickly surveying the ballroom. According to Endeavor, this was an opportunity to schmooze with HPSC board members and other upper elites, but he could not give less of a shit about rubbing elbows with these people. Sure, they had money and power, but their orders were given from behind the safety of a desk or a screen. Most of them had never even fought a real villain. Hard fucking pass.

Even though he suspected Izuku felt the same, especially with whatever misgiving he had about the event in general, he was too damn polite to openly snub anyone. So Katsuki found a quiet, unobtrusive corner to hide in and observe as Izuku awkwardly greeted various corporate penguins, each more indistinguishable from the last.

Todoroki invited himself to the same corner as Katsuki's but at least he didn't try to force conversation. They passed the evening that way, with Izuku occasionally sneaking away to hide with them before his sense of responsibility overtook him again, and he steeled himself to meet yet more people.

Some hours later, several of their classmates arrived—required attendance as interns at other hero agencies. Izuku was swept away by that meathead Mirio as well as Uraraka and Asui, both dressed in an obscene amount of pink chiffon. The group spent an obnoxious amount of time with their heads together, whispering and frowning and exchanging secretive looks.

It was really pissing Katsuki off.

So when Izuku suddenly broke away from his friends with nods and handshakes before heading for the lobby, Katsuki scowled and stalked after him.

"Deku," he called, once they were away from the chatter in the ballroom.

Izuku paused and turned, a smile lighting up his face when he spotted Katsuki. Those big green eyes dropped to Katsuki's own suit—black, of course, and tailored to his measurements—before his gaze darted away, freckles lost against the flush of his cheeks.

"Kacchan," he said, his hand rising to rub at the back of his head. By now, his curls had reverted to a disheveled nest. "Are you heading out too?"

Katsuki wrenched his gaze away from how his suit jacket strained around the bicep of his raised arm—the nerd wouldn't be able to afford the fee if he returned the rental suit with a busted seam—and demanded, "What's wrong with you?"

He marched forward until he'd crowded Izuku against the banister of a staircase that led up to a mezzanine. Izuku's eyes widened, face going even redder, gaze flitting everywhere except on Katsuki.

"W-What do you mean?" Izuku asked, along with a forced laugh that grated along Katsuki's nerves. 

"Don't play dumb. You think I haven't noticed you whispering like gossiping middle schoolers with the others? The fuck are you hiding?" From me , went without saying.

Izuku's idiotic display of flailing hands abruptly stopped. He blinked once, realization tightening his jaw. Katsuki's eyes narrowed at the sudden shift, his curiosity piqued.

Then, Izuku swiftly looked around, like that wasn't a totally conspicuous thing to do, and grabbed Katsuki by the lapels of his jacket.

"Oi," he objected, ignoring the hot flash of something that ran through him at Izuku's manhandling. "Don't fucking wrinkle my suit."

Izuku didn't listen, though, hauling him across the lobby toward what might've been a coat closet. Resigned, Katsuki allowed himself to be pushed inside.

Once the door was shut, it became clear they weren't in a coat closet. It was too small, with only enough room for Izuku to shuffle around and face Katsuki, whose back was now pressed to the opposite wall. He glared at Izuku, who was alarmingly close.

He could smell the appalling evidence on both their suits of a night surrounded by too many people with expensive and excessive tastes—saccharine perfumes, woodsy colognes, brandy and champagne and smoky tobacco. But beneath all of that, beneath the crust of blended odors, there was Izuku. He didn't wear cologne, so he smelled of clean sweat, deodorant, and something fruity that might have been from the product he'd used in his hair.

It was distracting. Katsuki needed to get out of this fucking closet. (He would not deign to even acknowledge how on the nose that sounded.)

"So?" he snapped, discomfort sharpening the word. His palms were sweating, so he wiped them against his suit pants. The hag would roast him, but whatever, the suit needed dry cleaning anyway.

Izuku's throat bobbed as he swallowed. "Okay, so the whole thing about the HPSC wanting to help victims of irreversible curses…"

Katsuki went still, his pulse calming as he refocused on Izuku's words.

"Obviously there's a lot of information we don't know, but irreversible quirks have always been, w-well, irreversible , and up til now, the only known case in which permanent damage was actually reversed was with—"

"Eri," Katsuki said, recalling the kid who'd been all but adopted by the UA staff. Aizawa was keeping an eye on her as the only person able to counteract her quirk if it got out of hand.

"Yeah," Izuku said, sounding uneasy. The only light in the closet came from beyond the closed door, which cast a faint halo around his head. "I mean, I totally support them researching how to help victims, of course, and like I said, there's probably a lot we don't know, but the idea of experimentation makes me kind of nervous, you know, after what Eri went through, and it makes me wonder if they've got ulterior motives or if they're hoping to get their hands on Eri's quirk."

"Eraser Head would never let that happen," Katsuki said. He was pretty sure not a single person at UA would allow that to happen, present company included.

"I know, but… it just raised some red flags is all."

That made sense. Definitely something to bring up at their next meeting with All Might.

Katsuki waited but Izuku didn't continue. Apparently, he was done. But since Izuku was still just standing there, Katsuki shifted again, their chests brushing in the cramped space.

Fuck. They were really too damn close. Close enough that Katsuki could see the way Izuku's tongue darted out to dampen his bottom lip, even in the dim light. Close enough that he could tell when Izuku's stupidly big doe eyes lowered to Katsuki's mouth.

Yeah, it was getting way too stuffy in there. Katsuki reached for the door handle at the same time Izuku did, the result being neither of them succeeding. Instead, Izuku's back hit the door followed by Katsuki's chest hitting Izuku's, and their hips aligning in a way that lit a streak of fire racing along every point of contact.

With a hiss, Katsuki lurched away, but the narrow space didn't allow him to get far. Izuku's face had gone all red and mottled as he blindly groped for the knob. This time, when the door finally swung open, it was Katsuki fleeing as his heart thundered and his face burned.

III.

Fortunately, nothing came of Izuku's concerns about the HPSC's charity ball. Not so fortunately, that might have been because the President was killed by Re-Destro. Whatever the reason, it didn't much matter seeing as their first year at UA went to shit shortly after.

And yet, somehow, they'd all made it through, some less unscathed than others. Since they didn't get a summer vacation on account of the whole 'the world will end if we don't defeat All For One' thing, Aizawa decided to take them on a training expedition for their second year winter break.

They would head north for Hokkaido, where presumably they would try not to get buried beneath an avalanche. Or something. Katsuki didn't know the details.

Classes 2-A and 2-B had been shuffled into one of those fancy trains with private compartments that fit six average-sized people each but only two to four if they were pro-hero sized. Having arrived at the station last due to his physical therapy running late, Katsuki was forced to share a compartment with Aizawa and Vlad.

Aizawa was fine, but Katsuki didn't know much about 2-B's homeroom teacher, so he stuck to jamming his good arm against the wall and glaring out the window.

About an hour into the trip, someone knocked on the door to their compartment. A moment later, it slid open to reveal a frazzled-looking Izuku. Katsuki gave him a quick once over, frowning at the sheepish set of his shoulders, which were all bunched up around his ears.

"Sensei," Izuku said, before pausing at the sight of Katsuki. Katsuki raised one eyebrow at the reaction. Izuku seemed to shake himself and then continued. "Um, we have a situation."

Heaving a sigh, Aizawa rose from his seat like he was carrying a hundred pounds across his shoulders.

"I'll join you," Vlad said, standing as well.

The two teachers left the compartment, but Izuku lingered at the door. He looked from the corridor to the compartment, his fingers drumming restlessly against the wood.

"What?" Katsuki asked, rolling his eyes.

"I didn't see you get on so, um, I thought maybe you didn't make it on time. I'm glad I was wrong." Then, for some reason, Izuku stepped into the compartment and slid the door shut.

He'd removed his uniform jacket and rolled up the sleeves of his button-up. Despite the cold air outside, the train's heating system was on full blast. He smiled a little nervously, the action tugging at the scar along his right cheek, and sat down beside Katsuki, close enough that their knees knocked together.

Katsuki stiffened, his breath hitching. Did the nerd have no concept of personal space?

"What's the situation?" Katsuki asked. He didn't actually care, but he needed Izuku to fill the silence with his inane chatter because otherwise, he might notice how rigid Katsuki had suddenly become. His dry throat clicked as he swallowed, and his stomach felt like a hive of frenzied bees.

Snickering lightly, Izuku said, "Monoma copied Sero's quirk and then couldn't stop dispensing tape. They're all kind of… stuck."

Despite himself, Katsuki barked a loud laugh. "Fucking idiots."

"It was a dare. Monoma couldn't resist."

"Don't make excuses for them," Katsuki said, without any heat. "How'd you escape then?"

"I almost didn't," he said. His face went red, the blush stark against his scar, and then went redder still when Katsuki continued to stare at him. His hair had grown back from where it'd been shaved, concealing the other scar that ran down his scalp and forehead. With his sleeves rolled up, the full extent of what he'd gone through was laid bare across his exposed forearms, his hands, his fingers.

His chest ached, but after six months, Katsuki had learned to distinguish the difference between an emotional reaction and something actually being wrong with his heart.

Clearing his throat, Izuku stammered out, "B-but I guess I should go check on them."

Katsuki held back an objection—the teachers were handling it, after all—and watched as Izuku rose to leave.

Except then, for no discernible reason, Izuku's leg refused to step forward. Instead, his feet slipped out from beneath him, and Izuku turned just long enough to flash big, startled eyes at Katsuki before he tumbled backward to the compartment floor.

For some other indiscernible reason, Katsuki was dragged from his seat to go down with him. And with the compartment being narrow in nature, he could do little else than allow Izuku to soften his fall.

Izuku let out a pained oomph as Katsuki landed on top of him. With his back on the floor, Izuku blinked up at Katsuki, who was trying very hard not to freak out at finding himself plastered to the other boy's chest. Swearing, Katsuki tried to wiggle free, but their legs were tangled and he only had one functioning arm.

"The fuck did you do, Izuku?!" Katsuki demanded, trying to twist around to see why he couldn't move his legs.

A piece of tape, which must have been stuck to the side of Izuku's pants, was now also plastered to Katsuki's. Fucking fantastic.

"There's tape on you," Katsuki said with a groan.

"Oh." Izuku looked like he was trying to awaken a fire quirk with how red his face had become. "S-Sorry."

Katsuki scowled. Then, because he could no longer handle the way Izuku's body felt pressed up against his own—all hard muscle and soft skin and weirdly comfortable despite the awkward curves and planes, almost as if they were made to fit— Katsuki slammed his palm against the center of Izuku's chest and used him as leverage to lean back.

"Are you doing this on purpose?" Katsuki asked, sounding far too breathy and unable to keep from remembering the last time they'd been this close in such a narrow space—at the charity ball, in a stupidly small closet that Izuku had shoved them into, before either of them could've known what awaited them. Before war and apologies and shattered limbs (and dreams) and dying and—

"I swear I didn't know I had tape on me!" Izuku cried, voice an octave higher than usual as he tried in vain to find a grip along the slick leather seats so that he could haul them both upright.

It wasn't helping. If anything, trying to raise his arms on either side of Kastuki resulted only in squishing Katsuki more firmly against Izuku's pecs while also being sandwiched between his stupidly buff arms. Katsuki's stupid fucking arm, wedged against his side in a sling, was useless, and with the tape sealing their legs together, he was tempted to explode the floor or the side of the compartment and let himself be run over beneath the train alongside the remains of his dignity.

"Why would I put tape on you on purpose?" Izuku said, now trying to scoot them both toward the door.

Fuck no were they calling for more witnesses to Katsuki's humiliation.

"Not that," Katsuki snapped, thoroughly disgusted by the idea of sliding any further along the floor . When Izuku only looked more puzzled, though, Katsuki braced his weight on his one good arm and rolled his hips. "This."

They both froze. Katsuki's eyes went wide, a match to Izuku's, along with the flames of mortification burning in his face. What the fuck had he just done?

Fuck, fuck, fuck, fuck, fuck—

"Kacchan," Izuku said, his name no more than a whimper. Then rough fingers gripped the back of Katsuki's neck and yanked him down into a hard kiss.

Oh.

Katsuki went still, every instinct he possessed abandoning ship. This had never happened before. Fight or flight switched to stand-by. What the fuck was he supposed to do about being kissed?!

Tentatively, slowly, muscle by muscle, Katsuki allowed his body to relax into the kiss. Their mouths were clumsy and inexperienced, and it was really fucking weird , but his pulse was also racing, his stomach twisted into Deku-shaped knots, heart pounding blood and heat from his chest to spine to his hands. Everywhere their bodies touched burned and sparked as if his quirk was again bursting from his—

The door slid open.

"Problem children," came Aizawa's thoroughly put-out voice.

Thirty seconds and a dozen bruises later, Izuku was nursing a scorch mark to his chest and a hole in his pants, and Katsuki was stomping down the corridor, desperate to be anywhere else.

IV.

Because Katsuki was apparently cursed, Izuku couldn’t just pretend it never happened.

In fact, over the course of their week-long winter training—during which no one was buried beneath an avalanche, much to his disappointment—Izuku kept trying to get him alone. Katsuki somehow managed to avoid it, though, mostly by forcing one of their classmates to remain at his side at all times.

It wasn't that he hadn't liked kissing Izuku. In fact, it was the opposite. He'd wanted to kiss Izuku for months by that point, if he was being honest, and the fact Izuku had kissed him first was… well, he supposed if he had to put it in the simplest terms possible…

It made him happy. Really… really happy.

But that wasn't the point. The point was that they'd just won a war and they were both grappling with the aftermath—with reconstruction and rehabilitation, with what their paths to becoming pro heroes would look like now against an ever shifting political landscape, and especially how it looked like for Izuku, whose quirk had been reduced to embers.

Katsuki knew where he stood and what he wanted, both in regards to Izuku and his career. But he didn’t want Izuku to jump into something he might regret, something that might further complicate everything he was already dealing with.

He'd probably regret it someday, but right now, Katsuki would rather not know what it felt like to have Izuku, if it meant he would only have to give him up later. That kind of hurt wasn’t something his mending heart could take, and he wasn’t looking to die a second time.

Unfortunately, that damned nerd was really fucking persistent.

“Kacchan!”

Katsuki's boots stalled on the sidewalk, and he groaned as he looked over his shoulder. Izuku was drawing way too much attention as he flagged Katsuki down. Reluctantly, he stopped to wait for Izuku to catch up.

They had one weekend left before the end of winter break. He'd hoped for a reprieve from having to dodge Izuku, just a few days to sit with his thoughts and figure out what the fuck he could do to fix things without losing Izuku entirely.

Well. This confrontation was inevitable, so it might as well happen now rather than later.

“Thanks for waiting,” Izuku said as he came to a stop beside him, only slightly winded. “Can we talk?”

Without a word, Katsuki led them to an empty space, clear of passersby, beside the statue of a hero who’d died in the war. Similar statues had been erected all over the city, like sentinels still keeping watch.

He rested his back against the cold stone and gestured for Izuku to join him. He’d taken a walk in the hopes it might clear his head. So much for that. It was late enough now that much of the shopping crowd had shifted into the bar hopping crowd. Where they stood, though, was quiet enough for a conversation.

Their breaths left plumes of white in the chill air. It was cold, but not enough for snow, which was fine by him. He’d had enough of that in Hokkaido. He was bundled up under several warm layers, his bad arm snug in a sling beneath his coat.

Izuku gnawed on his bottom lip, seemingly working himself up to saying something. “Listen, I…”

“You don’t gotta apologize,” Katsuki said, sounding tired even to his own ears.

Izuku wrung his hands at his waist. He wasn’t wearing gloves. His knuckles were red and dry in the cold air, liable to crack and bleed if left uncovered for much longer. Izuku's arms already had shit circulation after all the damage they’d taken. Idiot.

With a sigh, Katsuki used his teeth to tug off his one glove before digging out the second glove from his coat pocket. He held out both to Izuku.

Izuku’s ears, which were exposed above his All Might themed scarf, went even redder. Then, with a smile that creased his eyes, he took the gloves, the tips of their fingers brushing. The nerd’s skin was frigid against his much warmer hand. He had to resist the urge to cover those crooked knuckles with his hand and gently activate his quirk.

Instead, he watched, his thoughts unusually quiet, as Izuku slipped the gloves on and then murmured, “I wasn't going to apologize.”

Uncertain how to take this, Katsuki defaulted to glaring.

“W-well, not for the reason you probably expect anyway,” he continued, rubbing his now-gloved palms together to generate more warmth.

“And what reason did you think I'd be expecting?”

No wonder Izuku’s hands were so cold—all the heat was in his face. Katsuki snorted at his expense, but he didn’t laugh, because every part of him was suddenly and acutely attuned to the words shaped by Izuku's mouth, straining and impatient and terrified of whatever Izuku was getting at.

Izuku stared determinedly down at his hands—or rather, his gloves. “You seemed to, um, to b-be okay with, you know, but I realized afterward that it probably wasn’t very, eheh… um, good?” 

Katsuki swallowed, something within him beginning to deflate, before a spark of indignation had him straightening again. “You saying I’m a bad kisser?!”

Flailing now, Izuku hurried to correct himself. “No no no! Kacchan was amazing, perfect really, your lips are really soft and you smell nice and your skin—”

“I get it!” Katsuki said, flustered and confused, his own face going hot.

“R-right, I just meant that, i-it probably wasn’t very good for you. It was my first… uh, well, I kind of just… smashed our faces together. So. Um. Yeah. Sorry. M-maybe I could… t-try again?” The last two words came out as a squeak.

Katsuki stared at the anxiety emanating from Izuku's body language, his own nerves slowly settling. Every objection or worry or fear that he’d used to delay having this conversation was forgotten in the face of Izuku’s big, watery eyes and his tentative but sweetly earnest smile. Fuck.

Swallowing thickly around the emotion attempting to block his throat, Katsuki said, “Izuku, I…”

Izuku's expression fell. “O-oh! Um. That was really presumptuous of me, oh god, I didn’t—I wasn’t—that is, if you don’t—”

“Let me finish!” Katsuki snarled, effectively shutting up the rambling nerd who was now looking horribly dejected. Katsuki hated it.

“Sorry,” Izuku whispered.

Filling his lungs with a deep breath of cold air, Katsuki rested his hand over his right arm, hidden beneath his coat. “I… I need you to be sure,” he said softly. “About… this. Me. I don’t do this sort of thing. So if we’re gonna… you know, date or whatever, then it’s gotta be all or nothing. So you better be sure because if you’re not—” 

The rest of his words were smothered by Izuku’s mouth. His lips were cold but his breaths were hot, the contrast sending chills across Katsuki’s skin. The other boy crowded him against the statue until they were once again pressed chest to chest, hips to hips. Even through their winter layers, the contact was thrilling.

“I’m sure,” Izuku mumbled against Katsuki’s lips. “So sure. So so sure. Thank you, Kacchan, I swear I've never been surer about anything before in my life, oh my god, does that mean you're mine? Kacchan, are you mine? Say you’ll be mine.”

Katsuki was damn well not going to say that, but he kissed him back with just as much enthusiasm, too much teeth, and a soft moan that sounded like the same thing anyway.

Izuku pressed somehow closer, overwhelming him with kisses and quick breaths and words too low and mumbling to understand beyond the desperate undertones. His hands cupped Katsuki’s face with aching gentleness even as his body, his hips, tried to erase every molecule of space between them.

Distantly, Katsuki thought he heard a whistle, and a part of him was still aware that they were in public and not even a little bit hidden from view. Most of him, though, couldn’t care less who was watching.  

V.

Almost three years after their first collision outside that manga shop, it was Katsuki who cornered Izuku after class.

He turned nineteen in a few weeks, and graduation loomed. They'd gotten really good at sneaking around.

Katsuki unceremoniously hauled Izuku into an empty classroom before slamming him against the wall. Their lips connected before their bodies, hungry and biting as he ground his hips against Izuku's in frantic little circles.

With a murmur of, "I want an early present," he nudged Izuku down to his knees.

Izuku went without protest, making short work of Katsuki's belt and pants to free his erection. He wasted no time, his tongue swirling around the head of Katsuki's cock. Then he swallowed him down, and Katsuki's eyes fluttered shut, his hips jerking deeper into that tight, wet heat.

Raising his fingers, Izuku found Katsuki's mouth and pressed gently against his bottom lip, asking for entrance. Katsuki hungrily parted his lips, sucking the digits into his mouth. His tongue wrapped around Izuku's fingers, licking at every knuckle and callus, every ridge of scar tissue and bump of crooked bone, coating it all with spit.

After a moment, Izuku withdrew his hand and moved it down between Katsuki's legs. As he continued bobbing on Katsuki's cock, intent on sucking him off in record time, his fingers nudged Katsuki's entrance. Pressing lightly at the tight furl of skin, Izuku massaged it with wet fingers, encouraging Katsuki to relax.

He tried, but it was near impossible with every pass over his hole, every tease of fingertips that dipped inside, too shallow, before withdrawing to caress his perineum. Katsuki grunted in protest even as thick digits glided along the crease of his ass and taint. Then, with a hum of satisfaction around Katsuki's erection, he pushed two fingers inside.

Katsuki moaned loudly, body shuddering from the sweet intrusion. "Sh-shit. Izuku."

He was being consumed by sensation on all sides, Izuku's fingers plunging deep, stretching him from the inside, relentless and steady, even as his mouth worked his dick. The back of Katsuki's head hit the wall beside the chalkboard with a thud, his mouth open as he panted helplessly. Pleasure was a fist around his core, tightening almost painfully.

Izuku pulled off his cock just long enough to lick up the shaft and the mess of spit and precum. “You’re so wet, Kacchan,” he murmured, slurping at the fat head and tonguing the slit. His fingers pressed against his prostate, and Katsuki gasped, jerking hard. “Here, too. So wet and tight and hot. But only for me. Right, Kacchan?”

“A-ah!” Katsuki gritted his teeth, pleasure cresting within him. “Don’t say things like that, you—fuck!”

His spined arched, and his hand tightening in Izuku's hair was the only warning he could manage. Izuku, the damned nerd, only sucked harder and shoved a third finger inside him.

Katsuki struggled to draw enough air as his body jerked and seized, filling Izuku's mouth. Izuku made a strangled, happy sound, sucking and licking until Katsuki's unsteady hand slid to his shoulder and squeezed for him to stop.

Finally, Izuku pulled back, mouth fastened tight around his sensitive length so as not to spill a single drop. Green eyes, nearly all pupils beneath the fan of dark lashes, met his own, and Katsuki audibly swallowed between his panting breaths.

Izuku's fingers slid from his body but not before his inner muscles clenched down, unwilling to release them. He wanted to feel full, wanted Izuku in and around him. With a close-mouthed grin, Izuku rose to his feet.

Katsuki could only watch, sagging boneless against the wall, as Izuku unbuckled his pants and shoved them down along with his boxers. He kicked them aside, and Katsuki somehow managed the coordination to do the same with his own pants, still pooled around his ankles. 

Then Izuku brought his hand to his mouth and parted his lips, letting his tongue hang loose as Katsuki's spend spilled into his palm. Those large, focused eyes never left Katsuki's.

It was disgusting. It was so fucking hot. Katsuki moaned and shifted his weight to part his thighs even further. His heart jackhammered against his ribs, and he spared only a thought for whether that was good for him before he bit down on his bottom lip and fucking whined to be filled. He'd long ago abandoned any pretense of not wanting Izuku in every way he could have him.

Izuku swore under his breath as he lowered his palm full of Katsuki's come to his neglected cock. They both watched, transfixed, breaths loud in the quiet classroom as Izuku rubbed the slick up and down his hard length. Cum spilled between his fingers, fell in thick dollops to gather around his balls, ran milky over his knuckles, and spattered the floor. It was a goddamn mess, and Katsuki wanted it inside him.

"Fucking disgusting," Katsuki said, even as he readily raised one leg so that Izuku could hook an elbow beneath his knee.

Angling his hips and jerking Katsuki's leg higher, Izuku positioned the sloppy head of his dick at Katsuki's entrance. Katsuki dug the nails of his good hand into his shoulder, squirming so he could rub his ass against the thick tip, aching for it to catch and push and—

With a huff, Izuku thrust, filling Katsuki in one smooth motion. Katsuki gasped, knees nearly buckling as his entire body tensed. He rested his right arm around Izuku's neck—it wasn't yet as strong as he needed it to be for fighting, but he could at least move it with ease now. Then he squeezed his eyes shut and sank his teeth into Izuku's shoulder through the white fabric of his uniform shirt.

"Sorry," Izuku whispered. His lips scalded the skin of Katsuki's neck, tongue lapping at his sweat.

"I'm fine." Katsuki gave a small roll of his hips. "Move."

Izuku seemed all too eager to obey. He drew back and shoved in again to the hilt.

"Fuuuuuck," Katsuki groaned, his raised leg clamping down around Izuku's back to urge him on. 

They clung to each other as Izuku moved, lifting Katsuki onto his toes with the force of his thrusts. Katsuki buried his face in Izuku's shoulder, the previous weeks of their grueling third-year workload dissolving into nothingness as the scent of Izuku and sex surrounded them. Nothing mattered beyond the slap of skin to skin, Izuku's breath harsh and damp against his neck, Izuku's fingers digging painfully into his hips, guiding him to meet his thrusts, fucking him down onto his cock.

Izuku nudged Katsuki's cheek until he lifted his head. Then he kissed him, drinking of Katsuki's taste and breath until Katsuki's lungs burned for air.

"God, I love you," Izuku whispered into Katsuki's mouth. His thrusts grew shorter, sharper, chasing his orgasm. “I love you. Fuck, I love you so much. All of you—everything, every part of you. So beautiful. So hot and tight and perfect. You feel so good. You always feel so good. A perfect ass. A perfect hole.”

Katsuki squeezed around him at the words. Even as incredible as he felt, his dick wasn't ready to come again so soon, but the need he reciprocated for Izuku went beyond physical release.

Izuku grunted and kissed him again, his body straining. His hips snapped forward hard, and he shuddered as he came, stomach tensing and thighs quivering. His arms tightened around Katsuki's waist as his mouth sucked gently at Katsuki's lips.

Then, with an exhausted sigh, he carefully lowered them to the floor.

He sank to his knees, Katsuki straddling his thighs, still filled with Izuku's softening dick. They pressed their foreheads together, gathering their breathing as they waited for their pulses to regulate.

Izuku lifted his clean hand, fingers dusting the curve of Katsuki's cheekbone before cupping his face. He placed a tender, reverent kiss on Katsuki's lips.

You're mine, Katsuki thought. No matter what happened after graduation, after his hero debut, after adulthood settled around them in a layer of jaded dust, this thing between them would never change. Izuku would always be his. His past, his (birthday) present, but also his forever.

~fin