Magic Fixes What Apologies Won't (слэш)

"Uh huh, and you're an ass. Look, just- don't go killing anyone, okay?"
That is an odd thing for a child to be- and, seriously, from what she can tell- asking an adult. Even odder asking it of Peter who, despite his interest in the macabre, is a fairly gentle soul by all accounts, at least, that she knows of, because he actually seems to be thinking about it.
"I make no promises," he finally says, softly, honestly, and Stiles just gives him a long hard look before sighing and nodding in understanding.
"Well, I guess it isn't fair to ask that of you, really, under the circumstances, so, how about... Don't kill anyone who doesn't deserve it- by my standards, not your own, you fucking psycho."
"Hey, I'm not that bad," Peter sniffs, and Stiles narrows his eyes, "anymore."
[Or: The one where Future Stiles and Future Peter astound everybody.]