Samifer

Samifer is a Slash ship between Lucifer and Sam Winchester in the Supernatural series.

Canon
Sam and Lucifer were actively enemies. Lucifer was constantly trying to get Sam to allow him to possess him, but Sam refused. It was only at the end, when Sam felt he had no choice, to agree to let Lucifer possess him. After a climactic showdown at the end of Season Five, Sam and Lucifer ended up going back into The Cage, which destroyed Sam mentally. In season 7, Lucifer appeared as Sam's hallucination, causing Sam to need to go to a mental hospital. In season 11, Lucifer persuaded Sam, Rowena, Castiel, Dean, and Crowley to let him out of the Cage. However, Sam did not agree to being possessed by Lucifer, so he possessed Castiel's body instead.