While I don't typically point this out due to not being dreadfully concerned with the characterization of my UTAU, the actual characters of Halt Tanner and Soledi Renje are both nonbinary. Halt is afab bigender (prefers she/her pronouns, though she does occasionally choose to present as masculine at which point he/him is preferable) and Soledi is afab demigirl, if not full-out agender, and she doesn't really give a butt about her pronouns. (Bari, the third of my core trio, is pretty simply cismale.)
I also help with/manage my sibling's amab (err, well, they're a demon, so they can actually change sex too) genderfluid UTAU, BLACK, whose voice is androgynous -- at about g+6 they're considered female, and at about g-6 they're considered male. At g0, they're neutral-gendered. Shiny. I have... really got to finish their oto one day...
Being nonbinary myself, I sort of end up making a lot of nonbinary characters... orz.