>>714534424
They're meant to be vague. Non-binary means neither gender (but they definitely are either a boy or a girl, gender pronoun shit is just self-deceit to try and ignore the little dangling dick)
It makes it easier for players to self-insert as Frisk if the player doesn't know if it's a boy or a girl.

I like thinking Frisk is a boy and Chara is a girl, because women have no empathy and are all psychopaths.