Another possible idea: Ranma/3x3Eyes crossover...

[GenocideHeart]

This is an idea that came to my mind while reading Trinetra (the current 3x3Eyes story arc in Italy).
Gui Yang Wang's Wu, Benares, has a habit of either recruiting or eliminating any potential threats to his 'master', and after killing what essentially amounts to a demigod, Ranma would crtainly qualify as a potential threat.
Things, however, would get more interesting when Yakumo and Parvati get involved, seeking for Ranma's assistance themselves, figuring that if he can kill a Phoenix demigod, he'd be definitely a great asset in battling the enormously powerful Benares and his cronies.
This, of course, can escalate into a very ugly conflict in very little time, as Benares isn't above using underhanded and dishonorable tactics if needed, even though he tends to be strangely honorable for a villain. Any and all of Ranma's acquaintances may well be threatened...
Just a random thought. I tend to listen to plot bunnies a little too much lately... *shrug*