Teenage delinquent Takeru Narihira has been having a recurring dream where he is chased by monsters, only for a mysterious girl to always rescue him. Having fallen in love with her, he promises her on their 1,999th meeting that he will be the one to save her the next time. But a motorcycle accident sends Takeru to Denji Heian-kyo—an alternate version of Japan's ancient capital with futuristic technology and the home of the girl from his dreams, Tsukiyima, who does not recognize him.However, a black mist soon descends upon the city, petrifying citizens and unleashing monsters called oni. Only the so-called onmyouji—sorcerers who wield mystical powers and pilot magical 'shikigami' suits—can fight them. When the mist returns, Takeru discovers that he has strange transformation powers and can resist the oni. But he and Tsukimiya are ultimately killed, and Takeru awakens in Denji Heian-kyo once again, this time two weeks before the appearance of the mist. Swearing to protect Tsukimiya at all costs, Takeru vows to become an onmyouji and change the future.