Potential by Shadow Rave
SM Crossover. Due to a lapse in the chaos of Ranma's life, Fate steps in to take advantage of the opportunity. Ranmachan finds herself playing host to a war of souls where a struggling Hotaru Tomoe is fighting for her very existence against Mistress 9.
Well he/she is in Saturn's fuku but Hotaru seem to be Saturn as well so I'm not sure if it count...
Lunar Eclipse by Jollywolfe
Youma dust has turned up all over Jubann, but the Senshi didn't do it, so who did. Bad description. sorry. Ranma shows up in chapter two. Ranma12xSailor Moon Not a RxAk pairing
He/she haven't been in a fuku yet but I can't see how Eclipse can be anyone but him/her.
Edit: ups I kind of messed up with the links, should be taken care of now...