In the story, Dean had ended up in the serentity verse, post the movie. He is taken on by the crew though they are wary of him at first. Lots of interesting plot plus a slash relationship that forms between Mal and Dean. I remember there is a scene where Dean and River go crawling through the bowls of the ship looking for protection runes because Dean is sure that even in the future there is supernatural threats and that shipmakers would still put protection runes on anything they built and he is right. I know there is also a scene where Kaylee gets possessed and Dean has to save her. Help would be appreciated.

ETA: Found, link inside the post. Go read. It's wonderful