Basically the precursor to the one I did a while back, with Twilight trying to give Vilkas a dead rat. Vilkas got picked on by Fenrir a lot as a kid. During one of their fights Twilight decided to jump in and help her "new friend" by just pouncing on Fenrir; except that her and Vilkas didn't even know each other. She was just the weird kid who was always getting in trouble and everyone else avoided. But by her logic, if you jump into a fight and help the kid who's losing, that makes them your friend for life. But, I guess, technically she was right; more than a decade later they're still best friends. Also, this is the source reason to Fenrir's hatred of her, because she temporarily knocked his reputation down from "though kid" to "the kid who got beat up by the weird girl"