Repent

In a world of failures and mistakes, where nothing can be undone, humans have always wanted to undo anything they can. Cas messes up every day, and things only get worse as his life continues. When he stumbles upon a hut in the middle of the woods, he learns that if he slays another human being, he can go back into time for an hour and undo or redo things and edit his life however he wishes. This new knowledge changes Cas and his life forever.