Derek would really like to say that it's not a habit he has, to crawl into Stiles's room through the window in the middle of the night. But with everything still going haywire in Beacon Hills, with Stiles still being only seventeen, and with the Sheriff barely read into all the supernatural, knocking on the front door at four in the morning is really not something that is an option. Especially when the cruiser is parked right outside the house.
When it's not, Derek knows that there's no point trying the front door. If Stiles is still awake, it's because of nightmares or because he's deep in the throes of research. Whether he is awake or he's fast asleep, he's not likely to answer the door anyway, knowing better than most that things in Beacon Hills tend to go bump in the night and more often than not, it's in a decidedly not fun way. He stated that enough times when others from the pack tried the decent route of knocking and waiting for Stiles to let them in.
"You're not vampires. None of you needs an invitation. Hell, when it's absolutely necessary, none of you wait for an invitation anyway,” Stiles told them all more than once.
So Derek doesn't bother. The window to Stiles's bedroom is always cracked open just enough for him to get in -- he knows exactly how to open it to break the mountain ash barrier that Stiles has around his room -- whether Stiles is awake or not. When he's not, Derek nudges him awake and then listens to incessant grumbling about lack of sleep for a few hours.
Today though, today he's pretty sure that Stiles will be asleep. It's been a long week and they finally managed to get rid of the ghoul from Scott's attic the day before. Everyone else has vanished to their homes or wherever -- Derek didn't ask, all he knew was that the loft was empty. But then he got a call from Peter, one that raised an alarm in Derek's head immediately and he knows that he needs to check the laptop that Peter's Bestiary is saved on. Only, the laptop's been at Stiles's place for weeks. So Derek runs over to the Stilinski house, climbs up the tree next to Stiles's window and slips inside.
It's not until he's closing the window again and feels the barrier around the room activate that he takes a deep breath and his knees buckle. Because the smell in the room, while not untypical of a teenager's personal space, is more intense than it ever was in Stiles's bedroom. Derek slowly turns around and his gaze lands on the bed.
There, in his full naked glory, is Stiles, starfished on the bed, hands hanging off the sides of the bed, legs open and bent at the knees, his bare ass up in the air, pale as ever. It's not even that it's the first time Derek's seen him naked. There was that one memorable night when they all went skinny dipping and Stiles was the first one to divebomb into the water.
What catches his eyes a few seconds later, while he's still catching his breath, is something he's pretty sure Stiles should have no legal way of getting. There, right next to Stiles's leg, is a flesh-colored dildo in a very realistic shape of a dick. it's a little longer than Derek's own cock but has about the same girth. It's also glistening with lube. The same lube that, when Derek's gaze wanders back to Stiles's ass, is smeared all over the cleft between his cheeks. Stiles's cock is hanging flaccid between his legs as soft snores fill the room, accompanied by Derek's own ragged breathing as he takes the sight in again. And then again, just to make sure he's not seeing things.
His teeth clench and he walks across the room, then stops at the foot of the bed, Stiles's spread and open and slick hole right in front of him.
He should walk away. Step back, get out the way he came in, never mention this to anyone, especially not Stiles.
But then Stiles's breath shudders, he smacks his lips in his sleep, and his ass clenches right as Derek is staring at it. And Derek can't. He spent almost two years reminding himself of the fact that Stiles is underage, that he's the Sheriff's son, that it doesn't matter how much he's flirting.
A second later, Stiles's hole clenches again, this time accompanied by a mumbled word that falls out of Stiles's mouth.
"D'rek," he says, barely clear enough to Derek's ears.
The straw of Derek's resistance breaks. He reaches out a hand and strokes a finger down the exposed cleft, wets it in the abundance of lube that's all over it, and then, without hesitating, he pushes it past the rim of Stiles's hole. It slides in easily and Derek lets out a quiet moan when he feels how stretched and open Stiles is, then another one when he imagines the dildo moving in and out of where his finger is.
Derek adds a second finger, still meeting barely any resistance as he moves them past the rim and almost all the way inside. This time though, Stiles clenches his walls around the fingers and Derek smells the first wave of arousal. He doesn't need to look to know that Stiles's cock is filling up. Definitely not when he pulls his hand away and then thrusts back in, palm down, the pads of his fingers deep enough to slide over Stiles's prostate. The scent in the room intensifies even more and Derek's cock is hard enough that it's pressing against the zipper of his jeans uncomfortably.
He opens the button and lowers his zipper just to give himself some relief. Lacking any additional barriers like underwear, his cock springs free and stands away from his body, pointing right towards Stiles, who's still -- Derek spares a second to be surprised by that -- fast asleep even as his body reacts to Derek's fingers fucking him.
When he adds a third finger and the rim is stretched around them as he thrusts them in, Stiles's ass clenches and Derek doesn't miss the loud moan from the sleeping boy. Then, again...
"D'rek," falls from Stiles's mouth, followed by a moan.
Derek can't. He tries to convince himself to walk away now, to not do anything else. But he can't. He pulls his fingers out of Stiles's hole, whimpers at the complaining whine and the way Stiles's ass clenches around nothing. Then he gets up on the bed and kneels between Stiles's legs.
Just a little, he thinks. Just the tip.
With that thought, he guides his cock to Stiles's hole and rubs the tip over the smears of lube. Then he spots the tube next to Stiles's dildo and he grabs it, then drizzles some more over his head, hissing at the coolness of it against his heated skin. A moment later, when he's spread the lube over his length, Derek tilts forward and presses his cock against Stiles's rim, then guides it in until Stiles's ass clenches around the head.
Derek moans and his resolve flees the moment he's wrapped in the slickness and warmth. Without hesitation, he reaches for Stiles's hips and pulls them back as he thrusts his hips forward, bottoming out in one move. When his balls slap against Stiles's, he takes a moment to breathe, to feel Stiles's hole tightening around him. Then, slowly, his hands on Stiles's hips to hold him steady, he starts to move, he pulls back a little at first, then thrusts in slowly. The next time, he pulls out almost all the way and then slams in, his breath whooshing out of him when he hears Stiles moan.
Within moments he finds a rhythm and fucks Stiles without hesitation, the friction of the hole around his cock driving him fast towards the edge.
He's close, so close when the sound that comes out of Stiles's mouth is different to the moans and occasional mumbles of Derek's name that Derek already know.
"Huh," Stiles says, sounding a lot like he's awake.
Derek panics and freezes, balls deep in Stiles's ass.
It sounds different now than when Derek heard his name muttered earlier. It sounds surprised and a little hopeful. Stiles clenches his ass and Derek whines, but he can't bring himself to move. Stiles's hand flails and pats down the bed until it lands on the dildo. He picks it up and brings it to his face, then his ass tightens again.
Derek still can't move, can't run away now that Stiles is awake.
"I hope it's you," Stiles whispers. "Was thinking about you earlier, imagining this was you," he says, his fingers closed around the dildo.
Derek shudders, his own fingers tight on Stiles's hips.
"Hoped that you'd come in and fuck me," Stiles says.
Finally, Derek manages to move. He pulls his hips back and then thrusts in, Stiles's protesting whine at Derek pulling out broken halfway when Derek's cock fills him again.
"Oh fuck yes," Stiles says and arches his back to push his ass against Derek. "Please."
There's less hesitation now that Stiles is awake. Less waiting and moving slowly as Derek resumes the thrusting from before Stiles woke up. He watches as Stiles drops the toy in front of his face and grips the sheets below him, then moans when Stiles turns his head, grabs the dildo again and pushes it into his mouth. There's nothing but muffled moans and whines, the slapping of skin as Derek thrusts deep inside Stiles's ass.
When he feels like he's getting close, Derek lets go of Stiles's hip and reaches around, then his fingers wrap around Stiles's hard and leaking cock.
"Come on," he says, stroking in time with the thrusts of his hips.
Stiles spits the dildo out, gasps, and then his whole body tenses and his cock starts to spurt come all over the sheets. His ass tightens just as Derek has bottomed out and the pressure tips him over the edge and he comes, still thrusting as he fills Stiles's hole with come, feeling it dribble out around his cock with each move.
When they finally both start catching their breath and Derek pulls his cock out, Stiles immediately rolls over, not caring about the come all over his bed, and he pulls Derek down, their faces crashing together in a slow but still heated kiss.