The Imperial Capital Onmyou School is a three-year boarding school that trains officers for the "Imperial Onmyou Bureau," a national demon-exorcism agency. Yakou, Issei, and Reiji are second-year students at this academy. One day, Reiji finds himself on the verge of expulsion after injuring the son of a military official. Yakou and Issei plead with the principal to save Reiji, but as a condition for overturning his expulsion, they are ordered to investigate and capture "Semimaru," a mysterious masked man who has been attacking the upper class...