I know of two fics that don't get far enough, but he'd eventually end up as a girl. Part time in mine Chaos in the Moon, and full time in Lord CBoD's Fun and Games.
In mine Ranma and Ryoga get him cursed to unlock the full potential of his powers. In Lord CBoD's as I understood it, Mamoru was Sailor Pluto, in that one not all the Senshi reincarnated as female.