In Bran Bal, Zidane actually asks the genomes why they look like they have distinct genders and they said that once they get souls they start aging and need to propagate in order to take over Gaia or something. So having biological sex is kind of necessary for that. And no, Zidane is just a nice guy who went out of his way to help out his brother, omg


That, and there's Himiko, who is clearly female.