Takeru Narihira is a lone wolf delinquent high schooler who spends his days fighting and avoiding friendships. He has been tormented by a recurring dream: a mysterious girl chased by monsters, who always rescues him. He falls in love with her and, on their 1,999th meeting, swears that next time he will be the one to save her. A sudden motorcycle accident sends Takeru tumbling off a cliff. When he regains consciousness, he finds himself in Denji Heian-kyo, a bizarre parallel universe where ancient Heian-kyo has evolved with futuristic technology. There, the girl from his dreams, Tsukimiya, exists as a real person—a revered dancer known as the once-in-a-millennium performer. Before Takeru can process his joy, a black mist called Yamikaoru descends on the city, petrifying citizens and unleashing monstrous entities known as Oni. Only onmyoji—sorcerers who command mystical shikigami suits—can fight them. Takeru discovers he possesses a strange transformation power, but he and Tsukimiya are killed by the Oni. He then awakens again in Denji Heian-kyo, this time two weeks before the mist first appeared. Realizing he has time-looped, Takeru vows to protect Tsukimiya and become an onmyoji. He seeks training under Abe no Seimei, the most powerful onmyoji in the city, and takes on the challenge of changing a seemingly fixed, tragic future.

The setting is Denji Heian-kyo, a visually striking fusion of Heian-era aesthetics and cyberpunk technology. The city is protected by a hierarchy of onmyoji who pilot shikigami—mechanical or spiritual constructs that enhance their combat abilities. The central conflict revolves around the recurring Yamikaoru disasters and the Oni that emerge from them, but as Takeru loops multiple times, he uncovers a deeper conspiracy: the world itself is a constructed stage for a repeated ritual called the Centennial Pandemonium, orchestrated by Seimei for reasons tied to a 1,000-year-old event. Takeru’s stubborn, honor-bound personality drives him to defy that predetermined cycle, even as the truth behind Denji Heian-kyo—and Tsukimiya’s own role—grows darker.

Main characters include Takeru Narihira, a hot-blooded delinquent with a strong sense of justice and a fierce devotion to Tsukimiya; Tsukimiya, a graceful yet enigmatic dancer who seems connected to the city's core mysteries; Abe no Seimei, the calm, calculating top onmyoji who initially mentors Takeru but hides the world’s grim secrets; Atsunaga, a serious elite onmyoji who becomes Takeru’s rival and training partner; and Yura, a hot-tempered, battle-oriented onmyoji who teams with Atsunaga. Supporting figures include the twin genius siblings Shino and Kazura, and the brute-force duo Iruka and Kajiki.

Notable narrative arcs include Takeru’s first accidental loop and his initial death, his training arc under Seimei’s harsh tutelage, his first time controlling the berserk “Yasha Mask” power during the Centennial Pandemonium, the revelation that Denji Heian-kyo is a sealed world where time repeats, and the final battle where Takeru and an allied Seimei face a transformed Tsukimiya who has become an avatars of the “Great Time Bird” that erases possibilities to enforce a single predetermined future. The story culminates in Takeru proving that the future can be rewritten through sheer will, breaking the cycle and forging a new path.