Now that the Game has been out for a while and I don't think I will spoil anything I will say this regarding Fire Emblem Three Houses. Byleth must actually be meant to be a woman, I say this because she was meant to be a vessel for a Goddess so the Goddess could be resurrected in that body, it would make no sense to pick a male body to create a goddess, they would have used a female so male Byleth isn't real.