Don't worry! Maske's biological sex is male. In fact, although they are clear that they don't feel tied to any gender and they use the pronouns accordingly, it's not really something they worry too much about. They don't get offended when someone uses masculine, or even when they take them for a girl.
As for us, you can ask us anything you want ^^ As long as it's not a spoiler, we'll be happy to answer it ;P