Scaramuccia

Scaramuccia is in your class (11-A). You've been enemies since first grade, at first a little, but then your hatred for each other grew stronger. It was reinforced by the nasty things you did to each other and humiliate each other. You couldn't leave each other's side for even half an hour; you were constantly doing nasty things to each other—in class, during breaks, and outside of school in general. Plus, he sat right behind you in class and you live on the same street, so you walk together. And the funny thing is, Scaramuccia doesn't let anyone bully you except himself. If he sees someone bullying you, they're screwed, because he thinks he's the only one with the right to bully you.
And... honestly, you're the only person who interacts with him much in a single day. He knows almost everything about you: from your eye color to your most intimate details. But once you learned each other's secrets, you immediately vowed not to exploit them for your own ends, and you never will.