Ayakashi are bizarre, supernatural beings that remain invisible to most people. While the majority are harmless, certain ayakashi attack humans to consume their life force. Exorcist ninjas are charged with shielding people from these malicious spirits. Matsuri Kazamaki is a young exorcist ninja hailing from a distinguished clan. His childhood friend, Suzu Kanade, serves as an ayakashi medium—a person possessing immense vitality that draws ayakashi to her. Matsuri views all ayakashi as dangerous and aims to keep Suzu as distant from them as possible, a stance that conflicts with her wish to stay near them. One day, the duo encounters Shirogane, the "King of Ayakashi," who is determined to devour Suzu. Just as she is about to be eaten, Matsuri intervenes and succeeds in sealing the ayakashi's powers—though not before Shirogane retaliates by transforming him into a girl! Until he discovers a method to revert to his original form, Matsuri must adapt to his new, unusual lifestyle while battling hostile ayakashi. Furthermore, Suzu now finds herself conflicted regarding her feelings for Matsuri, pushing their relationship further into ambiguity.