In Atelier City, an artisic haven filled with technological marvels, lies an underworld where monsters dwell. These monsters embody the dreams of humanity, their greatest hopes and worst fears. Stumbling into this underworld by accident, Allen Lee, an ordinary young man looking for wonder, encounters an odd woman said to be a potential inheritor of the title, "Grim Reaper".

With her scythe that can reap dreams and the newfound ability he teaches himself to harness the power of dreams, he decides to team up with the Grim Reaper's Inheritor and struggle through the two sides of the city as part-time adventurers for the fortune they both seek.

If one is not chosen, they simply must choose.