A few ideas. (M/F, M/M, Futa)

[gnoah]

One Left standing. (combat driven sexual arena with changing combatants)
At a school of combat students are pitted against each other in the final battle of the year.  Lots of different styles of combat all come together (imagine naruto with magic and knights and gunslingers)  But with a twist, the winner gets to fuck the loser.  They are all down for it, but the winner gets to run the fucking.  Then they are pitted against a new opponent who might just fuck them.  The battles would be sexy too and shortish so we can go a quick sexy fuck and move on to the next battle and fucking!

Shameless world (this idea is 100% from Irilinquent
The world is just like we know it now, except that laws were passes about 10 years ago allowing sexual behavior to be free to do in public and it has just taken off.  People fuck anywhere and everywhere, There is still rape but it actually has decreased as most people who want to have sex can just have it now.  Since this has become such a major part of the world its not uncommon to fuck in an interview for a job, They teach sex is school now, There is a whole branch of school sports devoted to it. All the standard game shows and sitcoms are gone and replaced by sexual ones. Its never spoken of but plenty of families now play at home.  All beaches are now nude beaches and it is considered prudish to wear a swimsuit.  I would love to play this!

Trip to Vegas
Two couples head to vegas on a trip, the husbands each have the hots for the other wife.  We would have to talk about the pairing but it would be a husband wife swap idea.  Or maybe a cuckold story with one guy just watches.

Meet up. (m/m)
Two married guys meet up to share pictures of their naked wives and end up giving each other a helping hand... or more.

Its medical (mom/son)
Sam had his hands pretty horribly hurt in an accident, they have all for the most part healed but he has no feeling or control over them, they are basically stone.  A new type of medicine is going to be tested on him and its a 4 week trial that could make everything like new, but it has to be seen all the way through.  A day into taking it Sam gets very sick and mom calls the doctor who explains they must not have read the warning statements that due to the way this medicine is made Sam need to ejaculate every day  or a buildup of a substance that could kill takes place.  Mom has to start thinking on her feel.

We are trapped in a game!(bro/sis, mom/son, dad, daughter, or friends if i have to)
Hanging out on a Sunday afternoon and we decide to check out what games are on the shelf, remembering that when grandpa passed away we got a whole lot of antique games from him we head down to the basement to see.  Finding one that looks interesting we open it up and find ourselves in a different world, and we find that we cannot get out until we beat the game.   I would like this to be somewhat roll based and the game play would be all sexual. 

Also any futa or incest idea please shoot me it, im always down!

[gnoah]

Bump - Added Its medical

[gnoah]

Bump - We are trapped in a game added