Afflicted with a heart condition, Meiji-era noblewoman Satoko is determined to secure a marriage that will benefit her family before she dies. But before she can realize her goal, she's targeted by a mysterious assassin named Shinpei. In a last-ditch effort to save her life, Satoko asks her would-be murderer to marry her. Her proposal isn't sincere, but unfortunately for her, Shinpei loves as intensely as he kills. Can Satoko find a way to break the engagement without losing her life?

Satoko and Shinpei head into town on an errand for Asagiri, the prostitute who rules Goddess Island from the shadows. As the two of them spend time alone together, Satoko begins to understand Shinpei more deeply, and her feelings for him blossom. Meanwhile, fueled by jealousy and his duty as an attendant, Kotaro makes his move and tries to forcefully pull Satoko away from Shinpei.