He wanted to sing Vampire but it's too sexual for a straight male. He can genderbend himself via transformation magically (her name is Sanya), been in his lore for years after joking that women are more popular than men so he should go babiniku, and he got a Live2D teased on April fools 2020. Then he didn't use it because he's fucking lazy (for instance he was one of the first to get 3.0 after the first wave of 3.0 and he still hasn't showed it off, and he's so behind on milestone celebrations he only celebrated 400k subs on Halloween).
For advertisement for his birthday, Anycolor showed the full model of Sanya in train stations in Japan without his permission. Then, he brought her out on Halloween, dropped that cover (that's a euphemism for sucking dick) and looked at his tag where his fans posted pictures where majority of them were super hot Japanese women.
Also, Sanya canonically does not wear underwear or bras.