Takeru Narihira is a modern-era high school student, a lone wolf delinquent who channels his days into street fights and actively shuns friendships. He is haunted by 1,999 recurring dreams featuring a captivating, mysterious girl named Tsukimiya.

An accidental fall from a cliff unexpectedly transports Takeru to a parallel world: Denji Heian-kyo. This realm presents a futuristic fusion of technology and mysticism, reimagining the ancient capital. There, he discovers Tsukimiya is startlingly real, confirming the link between his dreams and this reality.

Shortly after this revelation, the lethal black mist Yamikaoru descends, unleashing monstrous Oni. The attack claims both Takeru and Tsukimiya. Yet, Takeru awakens once more in Denji Heian-kyo, recognizing he has slipped backward through time.

Determined to alter fate and prevent Tsukimiya's death, Takeru resolves to defy destiny. He seeks out the legendary protector of this world, the onmyoji Abe no Seimei. Under Seimei's guidance, Takeru begins training in the art of onmyou-jutsu, striving to become an onmyoji himself.

His personality is defined by a strong sense of justice and an unwavering, headstrong nature. Once committed to a goal, he burns with relentless determination, charging forward without hesitation. This drives his mission to uncover Denji Heian-kyo's truths and rewrite Tsukimiya's doomed future.