The mutations appeared early - creatures experiencing extreme skin deformations and manifesting strange new organs and tentacle-like appendages. It was thought to be some form of virus, or perhaps an alien cellular form that had somehow survived a meteorite impact on Earth.
Terrestrial creatures afflicted with the mutations were highly sexually charged and very aggressive - seeking to infect new victims through any and all forms of prolonged sexual contact. Their new organs were perfectly adapted to subduing their prey sexually - species have been cataloged with various forms of paralytic and aphrodisiac qualities in saliva, ejaculates and even in their sweat.
The authorities thought the virus was contained, but outbreaks began to appear all over the world, well outside of the containment areas. Before long the strain of the mutant outbreaks took it's toll on society and things began to break down. Today civilization lies in ruins and new, sexually predatory forms of mutated creatures pop up almost every week.
Since the threat manifested, a small enclave of scientists and military tried to synthesize a cure. Unfortunately the genetics of the mutations were too complex to cure completely - but there is hope. They have managed to synthesize a "day after" pill that will cancel the infection of anyone assaulted by the mutants.
The task now is to venture out into the broken world and rally anyone who remains uninfected, distributing the medicine that can stop the spread of the tentacle plague. Can our heroes help a world on the brink of full-scale tentacle rape?
So there's a setting we can play with. We could be refugees, members of the Enclave, folks recently infected - you name it. Wanna come play in the lusty apocalypse with me?
Send me a PM!