During the Shouwa era in Japan, greed spreads unchecked through the nation's bustling cities and communities. Enma Daiou, the King of Hell, summons an envoy to his office in the form of a small boy named Kurayami Santa. Through Enma's briefing, Santa learns that the volume of greed and selfish behavior generated by humans will soon cause a massive wave of souls to enter Hell simultaneously, a scenario that would be catastrophic for Hell itself. Santa is assigned a single mission: address the issue. Lacking any guidelines or rules, Santa is tasked with handling the situation as he deems appropriate. In the human world, a violent thunderstorm strikes a nearby cemetery with a bolt of lightning, and the envoy of Hell appears. Teleported into the human world, Santa quickly realizes that humans are just as wicked as Enma had described. Without disrupting the balance between light and dark, Santa begins his quest to complete the mission from Hell and restore order to the human world.