In Atelier City, a place 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 encounters a young woman said to be a potential inheritor of the title, "Grim Reaper". With her scythe that can reap dreams and his newfound ability to use the power of dreams, the two struggle through the two sides of the city as part-time adventurers.