I have two ideas, very basic that the individual partner could help plot more with. Please take a look at my O/O's first. I only do MxM, and only as the more submissive character. (That doesn't mean you have to be a harsh evil dom though.)
Pirated Away: A famous pirate and his crew attacked the town, stealing and raiding many of it's goods! Most fear for their lives, but the tales are true. This pirate kills no one as long as they are honorable, truthful, and don't resist. The lives of the people are spared, however their belongings are not as the pirate captain and his crew set sail. Little to their knowledge, a young stow away is on board!
The stow away would be my character, a poor citizen who can't seem to get a job anywhere. He's always getting attitude with customers or starting fights with clients, thus, gets fired every time. However, he'll learn that pirates deal with attitude a bit differently.
Notes: Fantasy-based pirates. NC or Bondage. Plot can be modified a bit with the exception of the stow away on a pirate ship. (Thus, your charry could be harsher, funnier, whatever you want to make up!)
Forbidden night! : One summer night, a village is attacked by a lone demon who is looking for something in particular. Having not found anything, he moves on. A child, around the age of ten, is the only one left alive after hiding amongst some hay in the stables. He sees the demon as he leaves, but instead of being angry, wants to thank the demons. The villagers hated him, as two were his step parents who worked him to the bone after all. He cared not for their deaths. He ran after the demon, but he is gone.
Many years later, that child is an adult and hears rumors of a demon. The description fits the humanoid demon, so he runs off to meet him and thank him, even if the demon doesn't remember. Though to both their surprises, the human had what the demon wanted all these years!
Notes: NC or Bondage. Fantasy, preferably in feudal Japan era. (Like Inuyasha setting perhaps?) But could be an old England setting or something. The item can vary though I was thinking it be a gem of some sort tied to a necklace the human had. Maybe he found it many years ago. Not entirely sure, so lets plot?
Any other plots you can think of involving pirates, demons, or elves!