I dunno. Guess someone just...decided. Probably because I was the second one? I mean, they can't name me One if there's already a One, you know?

[She doesn't remember their parents or they simply poofed into existence. They've always had their names and none of them have ever thought to change it. It's also because-

She runs her hand over her forehead, pulling back her bangs to show the 'II' prominently tattooed there.]

Also this weird birthmark. Bet that had something to do with it too.