A while back, I was in a game with this exact premise. Ended up not working out, but what the hell, I figured why not give it a shot myself?
So the game takes place in what could be considered an AU of Puella Magi Madoka Magica. If you haven't seen it GOOD YOU'RE SAVING YOURSELF SO MUCH HEARTACHE OHMIGODTEARSAHHHHHHHHHHHHHHHHHHHHHHHH
Ahem. I mean, it's a very dark Deconstruction of all things magical girl...and has next to no bearing on this particular game. Most of what's being kept is the idea of girls who make a wish with a particular magical creature becoming, well, magical girls. In OUR world, this means they become a Futanari, and gain access to essentially Pathfinder class levels. I use Pathfinder because it's what I like, damnit. The dungeons will be the constructs of various Witches, which the party must go into and defeat.
However, things are a little different, even in the dungeon. You guys attack as normal, but the monsters are...well they're trying to sex you up, basically. The mechanics behind their attacks are as normal, but the actual, 'shit I describe to you' is all sexual. Expect lots of futa enemies.
EDIT: I forgot the most important part! In Madoka, the girls had to 'cleanse' themselves with Chaos Seeds, well here, it's different-you 'cleanse' by, well, sex. Why? Because I'm a pervert that loves futanari sex, that's why!
EDIT 2: Abilities scored will be done with 20 point point buy. HP after 1st level will be rolled, but if you roll under half the max number on the die, you get half the max number on the die (for instance, rolling a d10 and roll a 3 for health? You get 5 HP plus Con). Start at 3rd level.
So, do I have any takers? Feel free to ask questions!