It's Where My Demons Hide

"You get out of him, right now!" Sam charged towards the demon inside Dean, but Castiel put his arms out as a barricade. "Sam, that is Dean." Dean flashed an eerie smile, black eyes glistening with hate. "Heya, Sammy." Demon!Dean fic! Set in season 9 after Dean gets the Mark of Cain. These are the potential consequences. T cuz of Winshesters getting saucy... And bloody.