Derek Hale knows how to fight.
Part of it is inborn. Wolf instinct. Clawing someone so that they let go of their holds. Ripping flesh out with his teeth, drawing blood. Snapping down on thin skin and not letting go until they fall down limp.
Part of it is due to training. He remembers hand-to-hand combat lessons with his father and uncles and cousins. He remembers sparring with Laura, and her kicking his ass with her nimble feet. He remembers running faster and faster, and learning how to shift and control himself so that he's in optimal condition to kill.
He knows how to deal with pain, knows how to concentrate on the white spots of hurt until they shrink and go away. Broken bones heal quickly.
It takes Derek a few more years and a cruel lesson in what he thought was love to realize that broken hearts don't.
Then Scott happens. Then his uncle Peter goes crazy, and Kate comes back to die. Then he has the pack, his four misfits. And Stiles. He has Stiles, the boy who won't shut up, the boy who tests every ounce of Derek's control in every single way. It didn't use to matter; Derek deals with it like he deals with grief. He hides it, sweeps it under his skin and in the space between his heart and brain so that he can focus on the now, on the kanima, on the Argents and the dangers to his pack.
But then they're in the police station. He's lying on his back, paralyzed and unable to do anything while Matt presses down onto Stiles's chest—Stiles, who has done nothing wrong except for wanting to help Scott, help Derek's pack—and Derek can't control the increased rhythm of his heart, cruel heat flooding his numb system while Stiles chokes for breath beneath the pressure of Matt's foot.
He can see himself roaring and leaping at Matt, can see his claws unsheathe and stab into the soft muscles of Matt's throat and chest and back, can smell the fear and desperation Matt'll show, like how Stiles is whimpering now.
But then Matt lets up, and the ache in Derek's bones recedes as Stiles breathes in.
It's almost a relief when Stiles's warm body falls onto his, when Derek can count the beats of Stiles's pulse.