Responses
I think that’s because even if you’re male as long as you’re chosen and accept to be the saintess you’ll lose all your previous identity and become her. So whoever you were before regardless of gender identity, personality or biology doesn’t matter. You become the saintess. Think of it like how Gozu was able to replace an existing character. If the character was female it wouldn’t matter since Gozu is ‘overwriting’ their identity and place in the world.

Wait wait, so Eve was actually the saintess, but was just switched with the role of demon king? And the saintess guy, was actually the demon king, but was switched roles with the saintess? But why is Eve still a guy, when he was actually the original saintess?