Depending on how you look at it, this might go against my statement in my turn-ons/turn-offs thread about not liking to ride on other people's ideas.
I should also preface by saying that even though I mention manga as my initial inspiration, it doesn't bother me if an interested player doesn't like or even outright HATES manga. I don't think my story idea has any distinctively anime/manga qualities.
Recently I was reading (in a manner of speaking) an untranslated hentai manga called "The Diary of Purimu," which incidentally I highly reccommend to any hentai fan out there. I didn't know exactly what it was about, since I don't read Japanese, but I assumed from the pictures and actions that it's probably about a succubus who falls in love with, or maybe just covets, a human who's somehow 'special' - I think maybe he has an unlimited source of sexual energy or something.
Regardless of whether this is what it's actually about or not, I thought that would be a really fun (read: sexy) RP. You'd be a succubus who's very experienced doing her job, and I'd play your most recent chosen prey, just some regular guy. But when you try to drain my life force (in the typical succubus fashion: sexual intercourse), you find I somehow have an unlimited supply no matter how hard you try to drain it all.
So, you repeatedly visit me since I can provide you with more energy than any other human being, but your 'boss' (a more powerful demon, maybe?) or fellow succubi quickly catch on to the fact that all of the energy you're harvesting comes the same source. So, you also have to protect me - and yourself - from another more powerful succubus who wants to steal your treasure.
Maybe it develops into a romantic relationship, maybe we just gradually become friends, or maybe you're just continuing to use me (though I find this last one to be the least preferable of the options), that just depends how it goes or where you and I want it to go. Regardless I think it'd be an interesting dynamic between a character who's frighteningly powerful and could easily destroy the other, and a character who the other would never want to hurt, even though he might not know it.
As I say in my turn-ons/offs, I prefer to do a lot of brainstorming with my potential RP partners before starting a story, so we can work out a lot of details together, such as the actual specifics involved with a succubus's 'job.'
So, if you're interested or have any ideas to build on mine, please take a look at my other turn-ons and offs to see if we'd get along and/or reply here and/or PM me.