A world where mysterious objects known as "Artifacts"capable of triggering phenomena that defy human understandinghave appeared. Humanity lives divided between two realms: the "Upper World," where a colossal city has been built, and the "Lower World," a vast and ruined wasteland. While carrying out a solo mission in the Lower World, Tezuka, a member of a special task force that collects these Artifacts, searches for clues to find his missing sister...