Brahne's one of many human victims of FFIX's committee of character designers. Like Amarant, she's got blue skin; like Steiner, her eyes have no irises. I reckon there were simply too many different artists involved in creating Gaia's population; it can't even manage a consistent idea of what counts as human. The only passable fanwank explanation I can concoct is the idea that there's been a lot of inter-species breeding in FFIX's world, leading to various traits being shared between races and nationalities over the years.