Allen Lee, a down-on-his-luck young man searching for something great to do with his life decides to move to Atelier City, a place filled with technological marvels and bright opportunities, but finds that his life there is nearly as mundane and unproductive as it was before. However, this changes when he somehow wanders into the Underworld itself and meets a strange girl he soon learns is a potential inheritor of the title, "The Grim Reaper". Bounded by coincidence, promises, and curses, the two decide to make the best of their fortune by traversing through the Underworld as part-time adventurers.