Sousei's sister

Latest chapter released translated on mangadex, and I think at this point it's probably safe to say he likely isn't related to the priestesses. Too bad because it was a cool fan theory.

So who do you think Sousei's sis might actually be? Not gonna lie, I'm kinda side-eyeing XX right now. We don't know if the dusters were human once yet or not, but we do know that Negi likes using colors to tie things together. So XX having red eyes is making me consider it lol.