The one I'm reccing here is one of the best I've ever read. It's set in X-Men movieverse, in a dystopian future, starring Pyro, and it's a work of absolute achy beauty. There's a small element of slash, but it's not the main focus of the story.
Title: The Fifth Monarchy
Rating: Mostly PG-13, with one rated-R scene towards the end.
Characters/pairing: John, Mystique
Summary: It's what you do after the apocalypse that counts. John, the open road, and living past the end of the world.
In the corners, the shadows grow long. John feels every year of his age, deep in the spaces between his bones. Seventeen was a long time ago.