Stiles is slamming into Derek at a ruthless pace, each thrust of his hips pushing the air from Derek's lungs, as if there's no room inside him for anything besides Stiles' cock.
And that's perfectly fine with Derek. He braces himself on his forearms, pulling his knees up tighter to change the angle, feels the heat coiling inside him, winding tightly as his muscles tense. He can feel the ridge of Stiles' dick, deep and hot, dragging against his prostate, every touch sending a shock of pleasure throughout his body. Derek moans when he comes, mouth going slack, eyes squeezed shut as his release pulses out of him in spurts with each shove of Stiles' cock.
"Oh, god," Stiles says, pace slowing just enough for him to really enjoy the aftershocks of Derek's orgasm. "I love feeling you come, squeezing around me while I'm still deep inside you."
Derek inhales sharply as Stiles rolls into him again, hitting every raw nerve ending. He opens his mouth against his own inner wrist, not quite biting, just pressing his teeth there to stifle a groan as Stiles continues to fuck into him.
With the post-orgasmic haze clearing from his mind, Derek is better able to focus on the feeling of Stiles behind him. The shallow dip of the mattress where their knees are pressed, the tenderness where Stiles' fingers are biting into Derek's hips. He won't have bruises to show for it–he never does–but there's a lasting impression Stiles leaves on his body regardless of Derek's accelerated healing ability. He clenches his muscles, earning a sharp hiss from Stiles as he slides back in, memorizing every ridge and vein in Stiles' thick cock.
Stiles pulls out, the slick slide feeling just as good to Derek now as it did when they first started tonight, the ridge of his cock head catching on Derek's rim and tugging before he slams back in again.
"Jesus Christ, Derek. How are you always so tight?" Stiles slides his hands up Derek's sides, pressing fingers between ribs and shoving into him over and over.
Derek wants to feel him throbbing inside him, wants to feel the swell of Stiles' dick, the warm, wet pulses of his release as he comes, fills Derek up. It's not that he wants it to be over. He knows they'll be at it again before the sun sets. He just wants that now, doesn't want to wait.
He reaches a hand back, fingers curling around the back of Stiles' thigh, and pulls him in harder.
"Come on. Come in me, Stiles. Give it to me."
And Stiles does. With a few more short strokes and his fingertips digging into Derek almost painfully, he groans, deep and low and almost animalistic, pulsing inside of Derek, and Derek can feel every twitch of his dick, every spurt of come slicking him up further from the inside as Stiles maintains his rhythm until finally he falters, stutters to a stop.
There’s a short moment of labored breathing, Stiles still gripping Derek's hips tightly, and then he pulls away, a wash of cold air brushing over Derek's skin. Stiles collapses onto the bed beside him wearing that smug, self-satisfied smile he gets sometimes.
"I'm giving you ten minutes, and then it's my turn to get pounded into the mattress," he says.
Derek smiles and pulls Stiles closer. "I'll give you five."