Onmyoudou magic was once a potent technique employed by the Japanese during the Second World War to gain the upper hand and establish their nation as a formidable force. However, Japan was swiftly defeated after the revered onmyouji Yakou Tsuchimikado triggered the "Great Spiritual Disaster," an event that continues to plague Tokyo to this day. Consequently, the Onmyou Agency was founded to exorcise further spiritual disasters and combat the demons that would enter the world. Today, Onmyoudou has become far more modern, simplified, and refined for use in a wide variety of applications, such as medicine and technology. Yet not everyone can utilize the magic, as is the case with Harutora, a member of the Tsuchimikado branch family. Despite an old promise to protect Natsume, the heir of the Tsuchimikado main family and Yakou's supposed reincarnation, as her familiar, Harutora lacks talent and chooses to live a normal life instead. But when a prominent member of the Onmyou Agency attempts to recreate the same experiment that led to Japan's downfall, he decides to honor his word and fight by Natsume's side.