Admittedly, Voice isn't a very developed character, but I'll come up with something solid once he's used. Yepp, Voice is a guy, but he works hard to look like a girl, simply because he's naturally a soft person and loves female clothing. (to simplify things, he's genderqueer and bisexual)

He's not human or only halfway so - he's some sort of demon/angel or spirit, but not malicious. He has several magical abilities all relating to sound and song.

Voice is calm but friendly and cheerful. When angered, he might go a little overboard with his powers which in turn causes him quite a bit of shame.