I don't know what's up with Relius' eyes, but I think I know why Ignis has birght blue eyes, while Nirvanas eyes are blank. I was thinking about this some time ago, and that's what I've came up with. I remember I've read somewhere that to create a Detonator doll, like Ignis and Nirvana, you need a soul full of hatred. In time when Nirvana still belonged to Celica, here eyes also were normal (had pupils and all, there was a picture somewhere on BlazBlue wiki). Later Celica freed the soul of the machine, and Nirvana was deactivated. When Relius had activated her again, he used soul of Ada, and it was probably not good enough, making Nirvana not fully functional (blank eyes). Later he crated second Detonator, and implanted her with soul of his wife, who was probably pretty pissed about him making a doll of their child, and that's what had made Detonator Ignis working right. That's why Relius also really is interested in Makoto's soul, because she has deeply hidden hatred, that was born in times when people were treating her like sh*t just because she is a beastkin. Of course it's just my speculation, so please don't take this as a fact.