One morning, office worker Haruka wakes up to find herself reincarnated as Eldora, the villainess in the hugely popular webtoon "Saintess Milia." Eldora is engaged to Emperor Oscar and is a notorious wicked woman who relentlessly torments Milia, the story's heroine... "Why did I have to be reincarnated as her?!" she laments. However, Haruka realizes that her “oshi”—the ill-fated Prince Levius—is scheduled to be executed by Oscar tomorrow. She becomes convinced that she was reincarnated to prevent her bias's death. With this conviction, Haruka successfully rescues Levius from the mansion besieged by Emperor Oscar's forces. But he is burdened by the false accusation of assassinating the previous emperor, has no place to go, no allies, and has resigned himself to death. In order to provide Levius with a safe haven, Haruka proposes a contract marriage: "Please marry me!" — A “oshi-katsu” girl reincarnated as a villainess x a cursed monster prince! Together, they will carve out their destiny in another world!