During World War II, the Japanese harnessed the ancient Onmyoudou magic to enhance their power, only to face defeat when a renowned onmyouji, Yakou Tsuchimikado, triggered the devastating 'Great Spiritual Disaster' in Tokyo. In the aftermath, the Onmyou Agency arose to avert similar calamities and battle encroaching demons. Today, Onmyoudou has evolved into a modern, versatile practice, applied in fields like medicine and technology. Harutora, a Tsuchimikado branch member lacking magical aptitude, reneges on his vow to safeguard Natsume, the main family heir and Yakou's rumored reincarnation, preferring an ordinary existence. However, when an Agency figure replicates the catastrophic experiment of the past, Harutora must honor his pledge and stand with Natsume in the impending conflict.