I don't think I ever figured out what Nagi was. I'm not entirely sure what Mashiro was. I'm sure they're related, and they're both connected to the whatchacallit, Tournament? Nagi seems to be some kind of Master of Ceremonies for the big HiME-offing contest; I have no idea whether he's even human, or ever was human.

I'm hoping to retain and make sense of more of that this time around. I have faith that there's a coherant backstory there, if I can just figure out what it is. (Or maybe not. Maybe he's just there, the way the Star was just there--an element of the story you're required to take for granted.)