It starts with Quidditch, specifically with a game dominated by how the Ravenclaw chaser and the Slytherin keeper are focused on little else but each other. Their rivalry is well-known by now, and Nishinoya is in the commentator's booth shouting excitedly about how the two captains are at each other's throats again.
Kuroo is pretty sure Nishinoya didn't mean at each other's throats in this particular sense.
Ravenclaw wins, and Oikawa hisses "slytherin locker room in an hour" over their handshake. They both know where this is going, but Kuroo is the only one who has the presence of mind to lock the door behind him. Oikawa doesn't waste any time.
It's not pretty. It's sloppy, teeth and tongues and spit everywhere and the lockers digging painfully into his back, and Kuroo manages to chuckle against Oikawa's lips, "you're really bad at this." It's not really true, but it'll make Oikawa mad, and there is nothing Kuroo loves more than making Oikawa mad.
Oikawa bites his lower lip hard, and Kuroo groans with delight, hooks his thumbs into Oikawa's Quidditch kit and yanks him flush against his body. Fuck - he's hard - they're both hard - Oikawa grinds his hips against Kuroo's, and Kuroo lets out a moan that's quickly muffled by Oikawa's tongue in his mouth.
His's dizzy with desire, and when Oikawa releases him, he sags back against the lockers. Oikawa's smile is saccharine.
"What'd you say about being bad at this, Kuroo-chan?" Oikawa asks, sugary-sweet like he always is at his most malicious.
"I think you should be the one up against these lockers," Kuroo says.
"That wasn't the- oh." Oikawa stops questioning it, because Kuroo has dropped to his knees in front of him and unbuckling his kit is suddenly much more pertinent.
It becomes a regular thing after that. Kuroo isn't sure if they can call themselves friends with benefits when they definitely aren't friends, but he's pretty sure it's general knowledge that they're fucking. Ravenclaw knows, at least. And he's overheard the two Slytherin Beaters, one with pink hair and the other with wavy brown but both with matching mischievous grins, ragging on Oikawa for sitting funny on his broom the day after sometimes. There are occasional snide comments from purebloods set in the old ways, but Kuroo and Oikawa are both seventh-years and reasonably popular, so they can generally shrug off the bigotry.
At any rate, Oikawa is comfortable enough to pinch Kuroo's butt sometimes as he passes him in the hall between classes. The first time he does it, Kuroo nearly yelps. He whirls around to see Oikawa striding down the hallway away from him, and even though he's facing away, the puff of his cheeks tells Kuroo that he's smiling.
From then on, there's more games - who can get the other to make the most embarrassing noises, who can figure out more of the other's kinks, who has the guts to send a booty call by Howler - which ultimately culminate in this situation.
Kuroo blinks. "I thought the deal was the victor gets to top?"
Oikawa is actually red-faced, and Kuroo is quickly caring less about their bet and more about the opportunity to see Oikawa flustered and begging under him. He leans forward over him, grabs a fistful of perfectly styled hair and yanks his head back so he can murmur against Oikawa's neck, "But if you don't want to…"
"Victor gets to choose," Oikawa manages, and rolls his hips up against Kuroo.
Oh.
"I wasn't about to - fuck - lose just so you'd fuck me," Oikawa explains between thrusts. "But that doesn't mean - ah - doesn't - shit, keep doing that-"
"Doesn't mean I'm not going to get what I want," he finishes once they've finished, and Kuroo nods like that makes sense.
He smells like Kuroo for the rest of the day, and it's intoxicating until Iwaizumi swats him and demands to know why he keeps sniffing his own arms. On his other side, Hanamaki and Matsukawa are snickering at him, and he flips them off before returning to his Potions homework.
Things start changing one day when Kuroo stops by Oikawa's usual study spot in the library and asks if he's busy and if not would he like to christen another aisle of history textbooks. Oikawa starts out with a quick "sorry, I have homework" and ends up going on a fifteen-minute tear about his Arithmancy professor's grading policy and really, an Arithmancy professor should have a better grasp of how a curve worked and Kuroo is nodding along and offering his own sarcastic commentary on the teacher that makes Oikawa feel much better than any soothing reassurance would've. Then Kuroo offers to help him out since Arithmancy is his best subject, and by the time they're done it's time for dinner and they really don't have any choice but to eat together and then after that they sprawl out in the beanbag chairs in the kids' section, working on homework with their ankles linked together and somehow having spent an entire afternoon and evening together without a single orgasm involved.
This realization hits Oikawa in the middle of a word and he bolts up like he's been electrocuted. "Did - did we just willingly spend not-sex time together?"
Kuroo looks up from his scroll. "It took you this long to figure that out?"
"Isn't that weird?"
"People do it all the time, you know."
"Weird for us, I mean."
"Nah, it's kind of nice, actually."
Oikawa flops back down on his beanbag and pretends his cheeks aren't heating up at that. "How are you so…?" He gestures vaguely at Kuroo's everything, knowing that the other boy will understand. "Like, all the time?"
Kuroo looks amused. "It's why you like me, isn't it?"
Oikawa cocked his head in false confusion. "Excuse me, did I ever say I liked you?"
"You didn't have to." Kuroo grins lopsided at him, and Oikawa's smile turns vicious.
"You know," he says conversationally, "you really piss me off."
"Prove it," Kuroo shoots back, and this is ground Oikawa is more comfortable on.
"Fuck you," Oikawa chirps through locked teeth and a happy smile.
Kuroo wiggles his eyebrows. "Later."
"I really don't know why I put up with you," Oikawa gasps, when it's later and Kuroo is balls deep as promised.
Kuroo is coated in sweat, and his hair is sticking to his skin in matted clumps. It wasn't a question, but he still suggests, "Cause I'm hot as hell?"
"Well, it's definitely not that," Oikawa mutters, and Kuroo snickers.
He thrusts with particular force, and a high noise flutters out of Oikawa's throat. Kuroo smirks at him. "Maybe that's why."
"I could get a whole drawerful of sex toys and and none of them would have a personality anywhere near as awful as yours."
"And yet, you haven't."
"Yes, Kuroo-chan," Oikawa says sweetly, "as I just said, I don't know why."
Kuroo hums contemplatively and hoists Oikawa's hips up a bit further. "I think it's cause we both like it like this. It's fun."
"Fun?"
"Yeah, fun. Don't you think so?"
Kuroo's movement slows, then pauses. For a moment, they stare at each other, then Oikawa grins, feral.
"It'd be a lot more fun if I were bent over that table."
A smirk crawled across Kuroo's face like a slime mold.
"I can work with that."
They always cuddle afterwards, "not because I like you," as Oikawa makes sure to tell him every time, but because they both love cuddling and their respective best friends are having none of it. At this point, the rest of Ravenclaw is used to finding the pretty Slytherin fast asleep in Kuroo's bed. The only real consequence they ever face is Akaashi annoyed that there's no way he can continue his previous six years of confidently informing Kuroo that he'll die a virgin.
Today, Oikawa is fucked-out enough to cuddle up into Kuroo's bare side and close his eyes almost immediately after they clean up and pull on sweatpants.
"This isn't because I like you," he says to Kuroo's nipple, just in case.
"You've mentioned," Kuroo tells a tuft of Oikawa's hair that's stuck up at an angle even he thinks is ridiculous.
Oikawa's hand that isn't pressed against his side sneaks up, searching, and Kuroo takes it in his own, twining their fingers together. Oikawa starts rubbing slow circles into his palm, and Kuroo lets out a pleased sigh.
"Man, I can tell you really hate me," he observes. Oikawa pauses and looks up at him with big, innocent chocolate eyes. "How do you put up with this much sex?"
"I just pretend your terrible hair isn't there and everything is perfect," Oikawa says blithely and plops his head back down onto Kuroo's chest.
The corner of Kuroo's mouth twitches. "You like the rest of me that much, huh?"
"Don't put those words in my mouth." Oikawa flicks the nearest part of Kuroo that he can reach, which is his sternum. Kuroo winces. "It's already had enough terrible things in it today."
"Why're you always so mean to me, Tooru?" asks Kuroo, then yawns hugely.
"Dunno." Oikawa starts dropping feathery kisses across Kuroo's chest. "Something about you just brings out the worst in me."
"That's fair."
Kuroo starts idly trailing his fingertips up and down Oikawa's back, and soon Oikawa is shivering with sensitivity again. Kuroo's fingertips skitter over his sides, and he lets out a startled giggle.
"Stop it, that tickles."
Of course Kuroo takes this as an invitation, because he's a sadistic little shit and he knows Oikawa doesn't really mind. Oikawa flails around halfheartedly, but for the most part, he's too worn out to do anything but lie there and suffer. Kuroo only lets up when his fingers find a particularly bad spot, Oikawa's head bumps sharply against his chin, and they both yelp with pain.
"I take it back," Oikawa announces. "This is why I'm mean to you. You deserve it."
"What did I ever do?" Kuroo asks, mock indignantly. He prods tenderly at the bruise that's forming on his chin.
"Would you like that list alphabetical or chronological?"
"You're kind of a dick, you know," Kuroo says fondly. He plants a kiss on the top of Oikawa's head.
"Mm, but you love it," Oikawa replies with absolute conviction.
"I do," Kuroo agrees, and then he's suppressing laughter as Oikawa buries his face in Kuroo's side.
All the provocation in Kuroo's arsenal, and yet it was only sincere compliments that ever made Oikawa really squirm.
"You're cute," he adds, half because it's true, half because Oikawa's even cuter when his blush reaches all the way to the tips of his ears. Oikawa knows exactly what Kuroo is doing. It still works.
"Oh, fuck off."