"You truly are a high-maintenance prince, aren't you?" Dohajae (도하재) lives as a Reaper (Saja) to atone for the sins accumulated when he was an evil spirit, taking lives with his own hands. The King of the Underworld (Yeomra) assigns him a new task: he must stay by the side of Hyeonjumin (현주민), protect him until the end of his natural life, and safely collect his soul. The terms of the contract are: 99 days, in exchange for his lost memories and the chance at reincarnation. To complete the mission, Dohajae begins a relationship with the ill-fated Hyeonjumin, acting as his guest, next-door neighbor, and school senior. Yet, he can't shake the feeling that there is something more that needs to be established between them.