I'm intersex spectrum so Every Bloody Time I run across some magical role in fiction only being able to be filled by a certain gender my first thought is to ask to see the fine print on that.

You can write fluffy happy transition fic, maybe with an Oracle helping her kid transition with her magical healing powers. Or you can go the angst route, since it's pretty obvious that the Gods of Eos are a glorious collection of cack-handed incompetents who'd probably set the rules in the most shortsighted way possible.

Either way, I just want to see the Nox Fleurets trying to deal with this rather impractical inheritance law.