The morning of Stiles’ fifteenth birthday he ends up between Derek’s legs, half shifted and mouthing Derek’s balls. He’s got pinprick claws digging into Derek’s thighs, and he knows his eyes are probably a yellow amber glow under the blankets. He can smell Derek, sleep sweaty and turned on, and he groans a little, licking at Derek’s sack, tasting.
Derek’s barely awake, his hands pressed against Stiles’s head, fingers digging into the base of his skull, keeping Stiles pressed up close.
“Fuck, your mouth.”
Derek’s voice is muffled through the duvet and Stiles squirms, pressing his ass back against the rough scratch of the cover. His own dick is already hard, hairless balls pulled up against his crotch, because he’s fifteen. He could come at a feather’s touch and be ready again right after.
Stiles blinks owlishly at Derek when the blankets are flipped back. He’s better suited to seeing in the dark when he’s half shifted like this, and it takes him a second to adjust, his tail flicking irritably.
He snuffles back under Derek’s balls, licking, spit slicking down his chin. Derek spreads his legs more and Stiles whines, appreciative, and gets closer.
He loves how Derek smells, here. Musk and wolf, and arousal. When Stiles jerks himself off at night, hand shoved between his teeth to keep from yowling, this is what he pictures, what he imagines tasting and smelling.
“Want me to fuck you?” Derek asks him, and Stiles huffs out a laugh against Derek’s balls. Because uh, yeah. Pretty much always. “You have to come up here, then.”
Stiles pouts, pulling back and stretching out on the bed between Derek’s legs, rubbing his cock against the sheets. He could just do this, too, until he-
“You just gonna rut against the mattress till you come, Stiles? Are you that desperate?” Derek’s voice sounds amused, but there’s a heat underneath it, something challenging that makes Stiles rub a little harder and look up to meet Derek’s eyes.
Because fuck he is that desperate. He’s always that desperate around Derek. It pretty much takes all his willpower not to just bend over and let Derek mount him in front of everyone (and oh, his dick twitches and that’s going to require some further exploration) and now, here, in Derek’s bed, with Derek’s scent all over him, yeah. Yeah, he’s more than that desperate.
“Can I, just, like this? I’ll come like this and you can fuck me after, ok? I really need to come, Derek.” Stiles’ voice is hoarser than he’d expected and he kitten licks over the head of Derek’s cock, mindless.
“Don’t,” Derek says, and Stiles looks up, body arrested mid-movement, because Derek’s eyes are seeping into red, and Stiles might not be wolf, but he’s still were and more importantly pack and even more importantly Derek’s. He can’t do anything his alpha says he can’t.
Fucking cockblocking asshole alpha.
Stiles whines, pitiful, but he stops rubbing himself off against the sheets and kneels up instead. His cock is a painful shade of red, curved up till it’s tapping his belly. He fists his hands at his sides to keep from fisting his dick, and he winces when his claws prick his palms.
“You’re like a cat in heat,” Derek says, a little awed, and Stiles wants to roll his eyes, because cat jokes, but it’s hitting too close to home, because that’s what Stiles feels like; aching and desperate, mindlessly greedy for it.
Derek moves fast, sitting up and switching them, pushing Stiles face-first into the pillows. Stiles gets his knees under him and spreads his thighs wide, arching his ass up. The pillow smells like Derek (the whole bed smells like Derek, he smells like Derek) and Stiles buries his face in it, a pleased little shiver running down his spine.
“I don’t understand how you can be so tight,” Derek says behind him, and Stiles wiggles backwards when Derek spreads him open, one palm on both cheeks, thumbs digging into his crack to get him even wider. “Practically fucking virginal.”
Derek punctuates it by spitting at the top of Stiles’ ass, and Stiles feels it slick down his crack, feels Derek press it in with just the tip his thumb. Stiles is far from virginal, but Derek’s right, he’s so tight he might as well be. Fantastical werecat healing, probably. Not like Stiles is planning on asking anyone that question anytime soon.
Moot point, anyway, considering how good it feels to have Derek have to work him open enough to split him in half on his dick.
Stiles is too busy pushing back on Derek’s practically dry thumb to hear the tube of lube open, but he hisses when he feels the thick liquid hit his skin, cold. Derek works his ass open with his thumb, until he can get the lube pressed up against Stiles’ hole and work it right inside, in and out and god, Stiles is going to come from just one fucking thumb in his ass.
“Derek, more, fuck,” he pleads into the pillow and Stiles should know better than to push.
“If you’re not going to let me set the pace, then you’re going to regret it,” Derek answers, and Stiles doesn’t even have time to take it back, because Derek is hauling him backwards with one hand on his hip and fuck, Derek didn’t work up to two fingers, he just- “That’s three. You asked for more, Stiles. Is there a problem with this? Not enough?”
Stiles can feel Derek’s pinky resting against his ass, right against where he must be stretched, skin red and thin around Derek’s three fingers. The press of them burns, and instead of fucking his fingers in and out, Derek’s pressing, pulling Stiles’ ass apart. He pulls down towards Stiles’ balls and Stiles can feels his ass open up, and he knows (knows because Derek’s told him, shown him pictures snapped with Stiles’ own phone, or texted to him in the middle of dinner) that Derek can see inside, the slick, pink, lubed inside of Stiles’ ass.
Derek curses, and Stiles feels his breath against his ass, and then Derek’s licking, his tongue pressed against his fingers. There’s a grunt of frustration and then Stiles whines, because Derek does press the fourth finger in, not to tease, not anymore. Derek’s just trying to get at what he wants, to open Stiles up for him. Stiles can feel Derek’s tongue at the rim of his ass and inside, pressed against the taut skin just inside and then further in, and oh.
Derek’s tongue is too long to be just human, and the next time Stiles moves there are claws at his hip to keep him in place, and Stiles’ dick jerks because the only thing better than Derek fucking him is Derek fucking him shifted.
Stiles squirms again, trying to get Derek to work his tongue in further, trying to get another press of claws against his hip. He ends up getting both of those and a growl against his ass, even better.
Derek pulls his mouth back, and Stiles thinks, for a second, that Derek’s going to fist him (they’ve done it before, Derek’s whole hand inside him, knuckling his prostate and making Stiles’ dick drip come onto the sheets while he begged for more, for Derek’s dick too, his other hand, fill him up more) but Derek just keeps his fingers stretching, thumb catching on the rim when he twists.
“You want something, bitch?” Derek asks, and his voice is rough, words slurred against longer canines. He’s shifted back toward human a little more, Stiles assumes, or he wouldn’t be talking at all, but there’s still claws against the fragile, pink, wet skin of Stiles’ insides.
“Fuck me, please,” Stiles begs, and he bears down on Derek’s fingers.
“Maybe,” Derek says, easily. “Your little cock is dripping already, Stiles. You’re so hot for this. I could make you do anything I wanted, right now.”
Stiles nods into the pillow, because it’s too true, and Derek’s gotten him to do a lot of things he’d never considered hot, and a lot of things he’d just flat out never thought about. He doesn’t regret any of it. Fuck, he fucking comes in pants just dreaming about it.
He whines when Derek pulls his fingers out, and earns a slap across his asshole for it. He clenches, tries to close up, but he can’t, ass gaping a little from Derek working it over. It makes him pant into the pillow, makes him hotter for it.
“Look at that,” Derek says, and he spreads Stiles’ ass again, palming his cheeks open. “Bitch’s little tailhole won’t even close up anymore.”
Stiles whines out a plea and Derek listens, finally listens, holds Stiles’ tail up and out of the way, and then lines his dick up, head popping in easy against Stiles’ stretched out ass. Derek’s got a thick fucking dick, and Stiles can feel every inch of it, swear to god. When Derek’s finally in, balls pressed up against Stiles’ ass, Stiles shivers, clenching around him.
“You’ve got the hottest cunt, Stiles, fuck,” Derek says and Stiles laughs desperately into the pillow, because it shouldn’t make him almost come, but he’s figured out he’s a kinky little fucker, and Derek’s no better. He’s stroking the soft skin between the base of Stiles’ tail and his asshole, fucking in slow and steady, his balls smacking into Stiles’ own each time he bottoms out. He’s popping the head of his cock out when he pulls back, just to watch Stiles’ ass try to close. “You ready?”
Stiles doesn’t answer, can’t, because Derek’s sliding back in and this time the last few inches are a little harder, Derek’s knot swelling slowly. He pulls back, and Stiles breathes out, hard, but it doesn’t hurt yet. It’s more of a push the next time, and Derek pulls him back by the hips.
“Don’t move,” Derek says, and Stiles breathes hard, feeling the stretch of Derek’s knot where it pulls against the rim of his ass. Derek stops, and Stiles can feel the knot swell inside him, can feel the pulse of it inside his ass. He barely breathes, worried if he moves even a little, he’s going to lose it, going to fuck himself back onto Derek’s dick until he comes.
“Push,” Derek tells him, voice rough, and Stiles does, bears down until the thick width of Derek’s knot pops out of his ass. He makes a desperate noise; it hurts, hurts more when Derek pushes back in and makes him bear down again, the knot popping out, over and over until Stiles is loose enough that it’s barely a snag, the rough tug of Derek’s knot fucking in and out of him, stretching him as wide as a fist, leaving his ass gaping when Derek pulls all the way out. “Slut.”
Stiles whines, pitiful and high and Derek fucks a finger into his ass with his cock the next time, and tells Stiles he can come if he can do it without touching himself. Stiles spatters come onto the bedsheets, working his ass back on Derek’s knot, the finger he has inside him, riding the feeling of Derek taking him apart, and the smell of Derek surrounding him.
Derek holds still through Stiles’ orgasm, then slides his finger out, thrusts going rapid and jarring, making Stiles jerk and shiver through the aftermath. Derek comes inside him, marks him inside and out, come leaking out his loosened asshole.
Stiles breathes into the pillow while Derek pulls out, knot still swollen, catching the rim of his ass, and Stiles clenches, tries to keep Derek buried in him. Derek spreads him open instead, tugs his tail up out of the way and uses his hands to thumb Stiles’ ass cheeks apart, open up his hole. Stiles knows that Derek’s checking to make sure he’s not hurt, as much as he’s checking because it gets him off to wreck Stiles’ asshole and look at it after. Stiles knows it’s red, swollen and gaping, and smells like Derek now, come slicking the inside of his thighs.
Derek presses a kiss to one of Stiles’ asscheeks and Stiles slumps, sliding onto his side on the bed and grinning when Derek curls up behind him.
“Happy birthday,” Derek says, and Stiles purrs, pleased as hell.