Dean is a vocational hunter, while Buff is a stationary one. He constantly has to leave for jobs, but always returns to her. How long will it take before the situation wears on them both?
What if, Dean wasn't Dean? When he rose from the grave after selling his soul, it's not Dean that's walking around, but a demon. Who works with Ruby to nudge Sam in the right path to summon Lucifer. The perfect plan.