Ranma = Senshi Stand in.

[Kadunta]

datexan has the story "Ranma and the Outers" (M-rated). Ranma doesn't, however, get to fight as a Senshi at least in the chapters present there, so the actual match to the search criteria is a bit iffy.

[Spokavriel]

I wasn't sure if others would think it fit because they ended up pointing out he could fill in for a wife but it never really came to pass in what is written.