In fictional ancient Korea, Yi Gwak is a demon hunter who lost his lover, Yon-hwa, and colleagues of demon hunters in the past. He enters the Midheaven, a transitory place for spirits, only to find the spirit of Yon-hwa who has forgotten about him. His deceased former mentor, Ban-chu, masterminds a demonic rebellion in Midheaven, wishing to invade the living world.
