This term was coined by wulgendeur on tumblr, and is intended for use as an adjective. For example one would say "I'm Proxvir" but not "I'm a Proxvir".
Someone who is Proxvir may also identify with the term, ''Thirdgender'' due to the fact that this gender is on a plane not connected to the gender binary. It is a whole, single gender, that is masculine. This is not to be confused with demi-boy, because demi-boys tend to have some connection to the binary gender male.