Maybe it would be something like this:

Some multiverse eater started to take over dimensions, resulting into multiple universes and timelines to clash altogether. In the middle of this chaos, Kung Fu Man must fight his way through multiple worlds, amidst all the conflits around many legendary fighters, heroes and villains. He must gather their strenght, before the Multiverse Eater destroys all existance.

Sounds like Project X Zone, Super Robot Wars and The Subspace Emissary, except it's bad. But hey, maybe a MUGEN RPG would have a plot like that. But better, of course.