Amelia Watson, a seemingly clever detective along with her partners Gawr Gura and Ninomae Ina'nis decided to explore the Underworld because of extreme ennui. However, Hades recognized their actions and took it as an act of intrusion. As a result, the gates of hell were closed and they were trapped in the Underworld with pursuers trying to kill them. On their journey to the never-ending world of the undead, they met the tsundere grim reaper Mori Calliope and the phoenix Kiara Takanashi. They became friends and decided to help in their escape from the Underworld.