Nanaka, a woman in her thirties, runs a business as an exorcist—though in reality, it’s more like a jack-of-all-trades job. One day, she is asked to check on a distant relative and, upon arriving, encounters a mysterious young girl named Riru. Despite being an exorcist, most of her cases aren’t actually supernatural. Instead, she often finds herself dealing with terrifyingly twisted human affairs rather than ghosts. While investigating these eerie incidents and listening to her clients' troubles, she gradually realizes that her new assistant, Riru, possesses an uncanny talent—one that helps expose the darkest aspects of human nature. Riru, despite being only ten years old, speaks and acts with an unsettling level of maturity. Her ability to understand the thoughts of criminals, her chillingly accurate judgments, and her deep familiarity with the twisted minds of murderers all point to one unthinkable truth: Within this child resides the reincarnated soul of a serial killer who was executed in their past life.