Out of all the candidates I have no idea whose personality would fit Kronii 2.0 and a full on villain character. I can identify strong candidates for twins, and also for a loli with the IRyS crown, but... the others?
The giant rrat is Nina, she could pull it off, I just can't imagine she graduates on such good terms then immediately jumps ship.
Yes. There's a persistent rumor that they broke up since she stopped following him on Twitter and other socials. No confirmation though.