You’re cursed as human for a lifetime after being a god/goddess. You still posses powers but just human and mortal. You awake in a forest, the deeper you walk you accidentally step into a road, in which Dean runs you over.
The Winchesters including castiel gave up on finding solutions to getting rid of the mark of Cain. You are their last hope, a demon. One who is said to posses the ability to get rid of it.
You’re alone in the bunker with him after mysteriously appearing in the bunker. You’re a Goddess/God. During the Heaven/Hell war. You’re strangers to everyone in the bunker.