Papillon Rose is a perverted parody of Sailor Moon :3
Well, my basic idea would be a bit of a parody too - the invaders would arrive, from space/another dimension/Hell/wherever, and want to (generic evil goal), and to do so they need to gather (something) from lots of people. This could be in a similar way to the energy stealing of the first season of Sailor Moon, or it could be the search for Pure Hearts/Beautiful Dreams/Star Seeds from the later ones.
The big boss would have generals, and generals last for a handful of episodes each, each bringing out a monster of the day. These would, of course, be... themed differently to Sailor Moon.
One general would not only have tentacles, but also try to make every monster a tentacled one. Probably has an army of triffids... and Firefox recognises triffid as a word. That is nothing short of awesome. There'd also be the uniform/costume-fetish one, the BDSM one...
It'd likely be more than a bit silly, but I guarantee that your heroine will find herself in all sorts of difficult situations *grin*