I think Wazuki turned into a black innate due to FATE. Perhaps he was a white innate previously, until that little incident.
I kinda doubt the theory about Wazuki/Serge being Magus or whatever. I mean, sure, Serge wants to save Schala, but c'mon. She was one of the best characters in the game! Who wouldn't wanna save her? ;D
Plus, it would mean Schala/Kid married (yes, I've read they've gotten married) her brother or her nephew. Ew, just like Mystik said.