When a person dies, their soul leaves the body in the form of a butterfly and the body itself rots away quickly after. Ono lost his entire family in a plane crash fourteen years ago. But since this tragedy, the body of Senri, his twin sister, is still intact while the butterfly that contains her soul was stolen by a mysterious individual during the accident, leaving her unconscious and in a vegetative state. In order to get back his sister's butterfly, Ono joins the famous "Death Bureau," a state agency specialized in the capture, conservation and management of the butterflies before they disappear for good 49 days after their host's death. (Source: MU)