actually i'm pretty sure osana's gender is unknown. it's obvious osana isn't a girl, and their biological sex is male, but they're actually kind of on the non-binary spectrum. the subtitles once said they were a guy i think, but they did the same thing for crona from soul eater. i read somewhere that the japanese language has a non-binary-specific pronoun that doesn't exactly have an english translation, so a lot of times when a character like that comes around they're referred to as "he" in the subtitles and even dub. which doesn't exactly make sense cuz they could just use "they," but whatever.