Yi-gyeong is a delivery guy. He can never take off his helmet. Because he looks different, people force him never to take off his helmet. He is losing his confidence. One day, he visits a container for his delivery job. There he finds a mirror that leads to another world. He meets an odd creature in the mirror, which he defines as a demon. Thanks to it, he regains confidence and dares to take off his helmet. The consequences are despairing. He gets laid off and receives a final note from his landlord to vacate his place. In need of money, he reports the demon to a YouTuber, but it never shows up. Yi-gyeong cries, "Make a killing," and transfers to the other world, where he makes himself the demon's demon. (BYUN Gyuri)