Initially, he doesn’t even touch Stiles, fingers hovering nervously above his skin as he connects all the marks on Stiles’ body like a treasure map, mind going blank as he does.
Eventually, when Stiles learns this calms Derek down -maybe when he knows Derek has had a particularly stressful day - he cranks up the heater, crawls on top of their bed naked and leaves a little note beside him saying ‘knock yourself out, big guy’ with eye liner or a non permanent maker attached to it.
After a while, Stiles gets used to waking up, finding his entire body covered in lines and shapes, like a dot to dot puzzle, and every time he smiles, gets this warm, fuzzy feeling in his chest knowing he’s helped Derek somehow.
Derek isn’t good at talking, doesn’t always manage to say what’s bothering him at the time it’s bothering him, and the fact Stiles can help him - even unconscious and snoring - is a big deal to him. Seeing Derek asleep and smiling, rested, when he wakes up (and all because of little things on his body he’s always hated) makes him happier than he ever thought possible. And hey, maybe that’s selfish, but he doesn’t care; not when Derek kisses him the next morning, whispering 'thank you’ before turning over and falling back to sleep like he isn’t afraid of the bad dreams that might come, not when Stiles is there.