Over time, Katsuki had started to notice something about Deku. Something that didn’t mean shit to him at first, at least until he realized one day that this thing about Deku extended to him, which regrettably made it his business.
And this thing happened to be Deku’s rather obvious and intense obsession with breasts. Big ones, medium ones, small ones, but especially the big ones.
Of course, it hardly made Deku special to be gawking at Uraraka or Momo or Mei Hatsume’s generous assets - almost everyone around Katsuki had at some point, with the exception of Kirishima who was so cripplingly gay he couldn’t even appreciate a good pair of tits (not that Katsuki could judge him - he was just as bad, just less oblivious). What made Deku stand out was how obvious he was about it, and how nobody gave him shit about it like they did with Kaminari or Mineta because it was Deku and everybody fucking loved Deku and besides, he was just a teenage boy. Never mind that they were third years now and technically adults - Deku always got a damn free pass.
But Katsuki didn’t fucking care because it wasn’t his problem. Or at least it wasn’t until he started noticing Deku noticing him, and specifically, muscle that he’d acquired over his years of hard work and training.
Third year had been good to Katsuki. He’d gained two inches in height and 15 pounds of muscle, most of it in his upper body where the bulk of his quirk training was concentrated. None of his old shirts fit anymore and it was a pain in the ass but the pride he took in his physique outweighed any drawbacks. He was strong and hot as fuck and he knew it, but the problem was… fucking Deku knew it too.
First it was painfully un-subtle peeks in the locker room, but Katsuki could chalk those up to simple admiration - Deku was always staring at everyone, of course, and always taking mental notes to jot in his godforsaken notebooks later. But it soon became undeniably clear that Deku’s intentions weren’t purely of the scientific variety.
During joint training, Deku started blushing more and getting distracted with his constant staring at Katsuki’s chest. During classes and lunch, whenever the opportunity arose, Deku’s eyes darted down Katsuki’s shirt like perverted little lasers, just like Katsuki had seen him do to Uraraka and even Froppy before. But, unlike the others, Katsuki wasn’t about to give Deku a free fucking pass.
Every time he caught him staring, Katsuki would level the harshest and most murderous glare he could muster at him, and when Deku would glance up and notice he’d turn the color of a strawberry and look away so rapidly he probably gave himself whiplash. And then he’d avoid looking at Katsuki for the rest of the day.
But the next day, the cycle would always begin anew. And the bizarre thing was, after awhile it started to piss off Katsuki less and less and amuse him more and more, to the point where he started actively feeding into Deku’s obsession just to see the nerd flail and blush and short circuit on par with Denki.
He started changing next to Deku in the locker room, sidling up to him half naked and stretching and flexing before finally putting his shirt on, and Deku always looked as if he were ready to burst a blood vessel. Then he started wearing his old tank tops to spar, the ones that were two sizes too small now, and the effect was absolutely hilarious. Deku could barely string two coherent words together, let alone come even close to beating Katsuki. Then again, the little fucker seemed to like getting pinned down and coming within mere inches of Katsuki’s heaving pecs. (Not that Katsuki could blame him - he was human perfection, after all.)
Katsuki knew he should stop antagonizing the little shit but for some reason he just couldn’t. His bullying days were long behind him but he just didn’t know how to stop tormenting Deku, especially since each new reaction from him gave him a weirdly addicting high that he couldn’t help but chase. He kept slowly and gradually escalating things until they finally came to a head one night in an otherwise empty training room.
Late night training sessions had become their norm since the end of their first year, and while the frequency of them fluctuated, they always managed at least one or two nights a week. These days it was closer to three or four, mostly because Katsuki found them even more enjoyable now that he had yet another way of ensuring victory over the nerd.
On this particular night, Katsuki showed up in another one of his old too-tight tank tops and a pair of loose sweats, and Deku visibly gulped at the mere sight of him. Those big green eyes dipped down for a brief but telling second before darting back up and determinedly staying on Katsuki’s own eyes.
“Nerd,” Katsuki grunted, starting up his usual warm up stretches as Deku looked on. “Ready to lose?”
Deku flashed a competitive grin. “I don’t know, are you?”
Katsuki smirked darkly. “Yeah, we’ll see about that.”
It began like it always did, with Katsuki attacking first and Deku trying to predict his moves and gain the upper hand early on. But rather than eventually prove boring, their spars were always learning experiences and they always found weaknesses in one another that they hadn’t previously known they had. Katsuki hated Deku more than a little bit for always being able to shine a giant flashlight on his shortcomings, but without him Katsuki couldn’t improve the way he needed to. He needed Deku, loathe as he was to admit it.
And Deku needed him, too, but it was quickly becoming obvious that he needed something a little more… stimulating than mere fighting. In fact, Deku was a fucking mess.
Tonight his moves were sloppy, distracted, and half-assed to a degree that was unacceptable. He was also blushy more than usual and out of breath far earlier than he should have been, and every time Katsuki got too close Deku would literally squeak and dance away into safety. It was a lot more dodging than Katsuki was used to, but he wasn’t stupid - he knew damn well why Deku was so on edge.
So, naturally, Katsuki decided to make Deku’s suffering far worse.
After calling for a five minute break, Katsuki strolled over to grab his water bottle and take a long drink. He could feel Deku’s eyes on him from across the room, so he decided to kick things up a notch. He set down the bottle and then peeled off his tank top, making a show of it and hearing Deku’s resulting choke bounce off the walls way too loudly. He suppressed a grin and pretended to not even notice Deku’s existence, picking the water bottle back up and dumping half of it over his head, letting the water trickle down his chest and shoulders and even letting out a satisfied little groan as it cooled him off.
Then he turned his head and looked over his shoulder and caught Deku openly staring, red-faced and slack-jawed. Deku then immediately whirled around, tense and straight as a board as he all but vibrated with embarrassment. Katsuki grinned, almost feeling bad for the guy - but only almost. He enjoyed watching him squirm too much.
Bet he’d look even better on his knees.
Katsuki’s grin fell as he blinked the unexpected thought away, unsure where the hell that had come from. Ignoring it for the time being, Katsuki rolled his shoulders and stepped back towards Deku.
“C’mon, Deku, let’s get back to work.”
“Y-yeah, okay,” Deku replied weakly, finally turning back around and taking a deep breath as if to calm himself. He looked up at Katsuki but flushed and quickly stared down at the floor instead, clearly unsure what to do with his eyes now that miles and miles of (wet) bare skin were on display. Katsuki smirked lazily, finding every ounce of Deku’s discomfort absolutely delicious.
This time, Deku was the one to strike first. Katsuki dodged him easily and quickly fell back into their comfortable rhythm, their push and pull and traded barbs and parries feeling almost like home after three years spent honing one another’s skills. Katsuki got so caught up in the flow and his one-track mind of win, win, win, that he nearly forgot his less honorable intentions until Deku managed to pin him to a wall.
It caught Katsuki by surprise, but that wasn’t what gave him pause. What made him freeze was watching the way Deku’s eyes dropped down and widened when he realized his arm was pressed fully against Katsuki’s pecs, his right hand curled into a fist over the swell of one. It was the kind of skin to skin contact their spars never contained, and it sent an unexpected wave of heat down Katsuki’s spine.
Deku swallowed and shifted just slightly, and Katsuki gasped - Deku’s wrist brushed over his nipple accidentally, and the sensation flew straight down to his cock. Deku’s eyes flew up when he heard the gasp, and they stared at each other stupidly until Katsuki panicked and grabbed Deku’s arm with one hand and blasted off against the wall with his other. He propelled them into the middle of the room and then slammed Deku down on the mat, legs pinned under his knees and wrists next to his head in Katsuki’s grip, faces mere inches apart as they breathed hot and hard.
“I win,” Katsuki declared lowly, watching Deku’s eyes dart all over his face. Deku was frozen beneath him save for the erratic rise and fall of his chest, and Katsuki knew he should get up and call an end to their session, but… something kept him where he was.
“Kacchan,” Deku whispered, the word a soft plea on his lips as his gaze travelled down the column of Katsuki’s throat and to the pecs he couldn’t seem to get enough of. Katsuki watched him closely, noting the way that Deku licked his lips seemingly unconsciously, and it was then that his brain took a backseat to pure instinct.
“See something you like, Deku?”
Deku let out a soft wail and screwed his eyes shut, trying to cover his face with his arms but Katsuki still held them firmly to the floor. “Kacchan, please, I’m sorry, I never meant to -“
“Shit,” Katsuki chuckled, shifting slightly to get more comfortable on top of him while still keeping him immobile. “Breathe, nerd. M’not gonna rip your head off.”
Deku peeked a single eye open. “... You’re not?”
Katsuki scoffed. “I know you’ve got a thing for tits, Deku. The whole school knows it by now, too. You ain’t subtle.”
Deku’s eyes flew open wide, utterly horror struck. “ Whaaa -“
“But hey, we all got our shit, right?” Katsuki grinned, shrugging one shoulder. “And I can’t blame you for staring at me all the time. I’m hot as fuck. And let’s be honest - I’ve got the best tits in our class, aside from Ponytail.”
If Deku’s face got any redder, it would likely melt into a disgusting pile of oozing nerd. He stared at Katsuki in shock, opening his mouth and not managing to get a single coherent word out.
Katsuki was loving this.
“So, what is it, Deku, huh? You happy just looking, or do you wanna touch?”
Deku moaned. “ Oh my God, yes - I mean, not if - not if - oh God, I didn’t mean, I just -“
Katsuki laughed again. As much as he loved watching Deku suffer, he had to admit - he was fucking adorable like this. “Seriously, relax,” he replied, sitting back on Deku’s hips and then bringing his hand up, placing Deku’s palm squarely on his right pec. “If you want it that bad, all you gotta do is ask, stupid Deku.”
Once again, Deku went completely still with shock. Katsuki found himself stupidly surprised by how warm Deku’s palm was - of course it was warm, it was a fucking sweaty hand - and he swallowed down the sudden jolt of arousal that followed.
“Go ahead,” Katsuki added hoarsely, dropping his own hands and freeing Deku’s. “Feel me up.”
Deku already looked fucking wrecked . He breathed hard and noisily as he twitched his hand, just barely curling his fingers to cup the hard muscle beneath them, and Katsuki growled before slapping his own hand over Deku’s and groping himself with Deku’s hand. “Don’t be a fucking coward, Deku.”
“I-I’m sorry!” Deku squeaked, biting his lip. “I’ve never - never done this before.”
“None of the girls ever let you feel ‘em up?” Katsuki asked. “Not even Round Face?”
Deku shook his head vigorously. “No. I mean, I’ve never been told no or anything, I’ve just -“
“Never had the guts to ask,” Katsuki finished for him, rolling his eyes. Then he sighed and pulled Deku’s hand off of him, scooting back and off of Deku’s hips to sit on the floor. “Come here.”
Deku sat up, brows lifting. “Huh?”
Katsuki leaned back on his hands, pushing out his chest enticingly. “Come sit on my lap and do whatever you want with ‘em. I ain’t gonna sit here forever, though, so hurry the fuck up.”
Deku scrambled up and on to Katsuki’s lap so fast he almost laughed out loud. He didn’t, though, too busy eyeing Deku’s excited expression and pink cheeks and, down lower, the telltale bulge in his shorts. Horny little shit.
Straddling Katsuki’s hips, Deku reached out shaky, scarred hands only to stop at the last minute. “Wait. Kacchan… why are you doing this? Why are you letting me… touch you?”
Katsuki narrowed his eyes, not appreciating that particular question. Mostly because he didn’t fucking know and didn’t wanna think about it. “You wanna play 20 questions or you wanna fuckin’ touch me, dipshit?”
“Sorry!” Deku squeaked, springing into action at last. His trembling fingers landed on Katsuki’s abs and slowly, carefully slid upwards until they were spread across each pec. Deku’s hands were on the bigger side, but Katsuki was pleased to find that he was still more than one hand could fully grasp. Fuck yeah.
Deku cupped and squeezed, biting his lip and staring with such overt lust that Katsuki could feel his ego inflating. Maybe something else, too.
“God, Kacchan, they’re so big ,” Deku marveled. “And your skin is so smooth. So soft, but the muscle is so hard… ”
Katsuki opened his mouth to agree and boast about how amazing he was, but then one of Deku’s thumbs brushed over a hard nipple and he jolted sharply in surprise. Deku’s eyes flew up and their gazes locked, Katsuki’s cheeks flushing against his will, and then Deku had the gall to do it again. This time Katsuki gritted his teeth and tried to hide his reaction, but it was really no use.
“Does that feel good, Kacchan?” Deku asked, tone equally curious as it was aroused.
“Fuck off,” Katsuki grunted, but he didn’t make Deku stop. Instead he looked down and watched as Deku’s fingers played and experimented, gently kneading the firm muscles and squeezing here and there, sometimes his thumbs flicking at both nipples and other times his index and middle fingers gently tugging. What didn’t get a reaction, Deku backed off on, but what did get a quiet hiss or groan, he doubled down on and carefully watched Katsuki’s face to gauge his reaction.
Katsuki was hard as fuck now, to his everlasting shame, but holy shit he had no idea getting his tits played with would feel like this.
But he certainly wasn’t the only one affected. To the contrary, Deku was panting and tense and clearly dying of need, but he was also too scared to ask for anything more than what he was currently being given. Katsuki could tell what he wanted, judging by the way that Deku kept licking his lips and was all but drooling, and Katsuki didn’t feel like waiting for him to grow a pair and ask for it.
“Deku,” Katsuki murmured, “you wanna suck on them, don’t you?”
Deku’s face went up in flames, but to his credit he didn’t deny it. Instead he looked up at Katsuki through his lashes and asked shyly, “C-can I?”
Katsuki responded by threading his fingers into Deku’s hair and tugging him closer. “C’mon, do it.”
Deku groaned and dove in with both feet. At the first hot, wet slide of Deku’s tongue, Katsuki let out an honest to God moan for the first time. He couldn’t stop it from coming out and he was starting not to care, especially as Deku whimpered happily and swirled his tongue around one nipple while his fingers teased the other. Katsuki watched every second of it, brows furrowing and dick pulsing in his pants when Deku wrapped his lips around the hard nub and sucked.
“Fuck,” Katsuki shuddered, barely aware of the way he was gripping and pulling at Deku’s hair until Deku switched to his other pec, lavishing it with the same attention and beginning his torture anew. Deku also happened to shift in his lap just then, bringing their lower halves closer together, and all it took was a tiny thrust of Katsuki’s hips to make their clothed erections rub together.
“Oh God,” Deku panted against Katsuki’s skin, closing his eyes and dropping his forehead against his collarbone. “ Kacchan… ”
Katsuki’s hand slipped from Deku’s hair down to his ass without thinking twice, squeezing a firm cheek through his shorts and then rocking him down as Katsuki thrusted up. Deku gasped and his hands flew to Katsuki’s biceps for balance while Katsuki murmured, “Move with me, Deku.”
Deku complied beautifully, meeting him thrust for thrust and whining happily when Katsuki returned his hand to Deku’s hair to guide his mouth back to his chest. Deku’s inhibitions were fading fast as their pleasure increased, Deku licking and sucking at Katsuki’s sensitive nipples and rutting into his lap like the horny teenager he was, and it was all at once too much and not enough. Katsuki wanted to pin Deku to the floor and rip his clothes off and ravage him and make him scream, but he could feel himself already falling apart at the seams just from this.
Then there were teeth biting down and tugging carefully, experimentally, and Katsuki gasped and started moving harder, faster, and then Deku switched pecs and did it again, and Katsuki’s hand flew back to Deku’s ass to hold him still and rut against him nothing short of desperately. Deku broke away a moment later panting hard and raising his head to lay it on Katsuki’s shoulder, wrapping his arms around Katsuki’s neck as he threw everything he had into moving with him.
“ Kacchan,” Deku whispered, mouthing against Katsuki’s throat, daring to flick his tongue against the as-yet untouched flesh. “ Kacchan, it feels so good.”
Bypassing Deku’s shorts and boxers and finding the supple, soft flesh of that well-muscled ass, Katsuki squeezed hard and groaned, “Yeah, you gonna come for me, nerd? Gonna come in your fuckin’ pants for me?”
“ Yes, yes, yes,” Deku whimpered, tilting his head back with his eyes closed and letting the pleasure overtake him. Katsuki watched from mere centimeters away as Deku’s mouth fell open and his brows furrowed, the sweetest sounds he’d ever heard pouring from Deku’s lips as he shook and clung to him. It was all Katsuki needed to fall over that same edge, yanking Deku closer and burying his face in Deku’s neck as he came harder than he ever had by his own hand. He bit down into Deku’s skin to muffle his own noises, tasting a faint hint of copper and distantly hearing Deku’s moan of absolute delight.
For awhile, the world ceased to exist. Katsuki floated through the blissful haze of their afterglow, an embarrassingly long time passing by before he realized that Deku was now curled up in his lap and snuggling into his arms. Arms that were wrapped around him affectionately.
It was disgusting. And yet, Katsuki stayed there and kept holding Deku until he stirred and peeked up at Katsuki with wide, slightly fearful eyes, as if he had no idea what to expect now.
“... Kacchan, I -“
“Hush, nerd,” Katsuki murmured, not unkindly. He took a breath and glanced at the clock on the wall behind them. “It’s late. Should hit the showers before lights out.”
“Okay,” Deku replied softly. “Um… should we… talk about this, or -“
Katsuki scoffed, gently pushing Deku from his lap. He stood up and then held out a hand to Deku, helping him to his feet as he replied, “Don’t overthink it, nerd. We were both pent up. Doesn’t have to be a thing.”
Deku breathed a sigh of relief and offered Katsuki a slightly bashful but relieved smile. “Okay. Thanks, Kacchan.”
Katsuki rolled his eyes, stepping away to grab his tank from the floor. He’d pulled it back on and was stretching it down over his abs when he looked back at Deku over his shoulder and grinned, “If you wanna fuck around again, you know where to find me.”
Deku’s eyes went wide. “I - oh! Really?! Okay! I… I’d like that, Kacchan.”
Katsuki smirked and grabbed his water bottle, swaggering out of the training facilities without another look back.
“I know you would, nerd.”