In a world engulfed in darkness, evil spirits known as "eternals" roam freely, preying on humans. To protect humanity, spiritual beings called "spirit beasts" choose humans as their vessels, turning them into "Users" with special powers. Rika Moritaka, a 19-year-old awkward girl working as a pizza delivery driver, narrowly escapes death during a brutal attack by an eternal named Fizt. On the brink of death, Rika is saved by Greed, the most powerful spirit beast, who offers her a contract on the condition that Rika must give up one of her hands. Despite not joining the UF (User Federation), an organization formed to eradicate the eternals, Rika decides to act independently, navigating this dangerous world alongside Greed. Throughout her struggle, Rika begins to uncover dark secrets about the eternals and the mysteries that bind Greed to his past.
