Howl (The Demon Inside)

Merlin and Emrys just struck up a deal: Merlin gets to be in charge of his body for a few years while Emrys kicks back, relaxes, and pretends to be the human he isn't. It had been going perfectly too...until Merlin meets Arthur. Things tend to take a turn for the worst after that. Namely, Lucifer rising. possessed!Merlin, Hunter!Arthur, slash, pic inspired