Fadoms: Firefly, Highlander, Buffy, Pirates of the Caribbean (I believe it contains all of these & maybe more)
Wash dies (most likely because of Serenity movie) and someone (an immortal) finds him or goes looking for him knowing he is immortal. I think that it is Xander and that he lived with Wash when he was a kid knowing that he would one day become immortal. They take him away to a private world/moon to train him. He refuses to give up on his previous life. The planet is a dividing point between the human 'verse and the worlds inhabited by demons (don't think anyone other than those living there know this). Jack Sparrow runs a ship and has a moon inhabited by both demons and pirates. I think he finds a re-incarnated Will Turner.
Does any of this sound familiar?