Tachibana Shizuka is the human female protagonist. She endures a traumatic event when her fiancé, Eiji Kuraza, transforms into a demon, costing her an arm during the incident. This tragedy fuels her quest for answers and vengeance concerning Eiji's fate.

Seeking help, she approaches Tsunami Shijo, a guardian operating a detective agency specializing in demon extermination, requesting his aid to locate and eliminate her transformed lover. Her investigation into Eiji's demonification uncovers the cause: an experimental drug from a pharmaceutical company. Partnering with Tsunami, she confronts the demon leader Takamiya, responsible for distributing the transformative drug and orchestrating attacks on humans. Her motivation centers on understanding Eiji's fate and preventing further atrocities.

Her background is defined by the loss of her fiancé and her resulting physical and emotional trauma. She channels her grief into determined action, relentlessly pursuing the truth behind the demonic transformations. Her interactions with Tsunami form a pragmatic alliance focused solely on achieving justice for Eiji and stopping more victims. The narrative concludes her story within these OVA events.