The story takes place in the underworld of a fictional pseudo-European world. The underworld is not the hell in the traditional sense, but a place where all deceased souls eventually arrive. Throughout the long history of humanity, countless wars have claimed the lives of young people, and among them, World War I has become the largest source of souls in the underworld. When these souls arrive in the underworld, they do not disappear immediately; carrying unfulfilled promises, unspoken words, and unforgettable people, they linger between death and memory. At the center of the underworld lies a special tavern called The Last Memory, which is the final stop for the dead. The owner, Hades, is responsible for maintaining order among the souls; he does not punish the deceased, but helps them accept their death. And his partner, the most popular songstress in the underworld, is none other than Persephone's mother—a deity with special powers, who uses her singing to lead the dead into their most precious memory and help them bid a final farewell. There is an insurmountable boundary between the living and the dead: the living must not stay long in the underworld, and the ruler of the underworld must not show favor to the living. The order of the two worlds is maintained jointly by the divine covenant and Zeus, the king of the gods, while the ancient deity Cronus is lurking in the shadows, trying to tear apart the boundary between life and death, let the dead return to the human world, and make death a thing to be feared once again.
