Sōko Kiryū is a first-year high school student who has just moved to a new town. Troubled by frequent dizzy spells and a persistent sense of unease, she hopes to find stability in her new school. Instead, her striking beauty immediately makes her a target, and she is cornered in the infirmary by a male student named Kashii. When Kashii attempts to assault her, a terrifying, unexplainable event occurs: he simply vanishes into thin air, leaving only his clothes behind. The school soon forgets Kashii ever existed, and a mysterious young man appears in his place, claiming his identity. Only Sōko can see through the deception. This man reveals himself to be Akira of the Saionji family, the current incarnation of Byakko, the White Tiger of the West. He delivers a shattering truth: Sōko is not human. She is the latest reincarnation of Sōryū (also called Seiryū), the Azure Dragon of the East and the ancient demon queen who once commanded armies of oni that preyed upon humanity. It is Akira’s sacred duty, a role passed down through his bloodline for generations, to destroy her.

Set in modern Japan, the story pits Sōko not only against her destined killer but against her own emerging nature. She begins to manifest the signs of her demonic heritage: a growing horn on her forehead, an insatiable hunger for human life energy, and supernatural powers. While she rejects the label of a monster and desperately clings to her human memories and emotions, she cannot deny the evidence of her own body. Complicating everything is the intense, forbidden love that blossoms between her and Akira. Though he was born to be her enemy, Akira finds himself believing in her desire to remain human. Torn between his duty to his family and his feelings for Sōko, he chooses to betray his ancestral mission and help her find a way to break the cycle of reincarnation and transform into a normal girl.

Their quest for a cure places them at the center of a conflict that involves the other two guardians of the four cardinal directions, all based on the tale of the Four Gods. Sōko’s seemingly gentle brother, Takao, is revealed to be the powerful Genbu of the North, the Black Turtle. However, unlike Akira, Takao does not wish to kill Sōko; he is the one who artificially revived or cloned her from the original demon queen’s remains, intending for her to awaken fully and lead a new demon uprising. He is joined by Hiko, a clone of Sōryū’s sister, who also pressures Sōko to embrace her dark destiny. As Sōko and Akira investigate ancient ruins and the forgotten history of the demon clans, they seek a method to extract the Sōryū essence from her body. Throughout the story, they must evade and battle the machinations of the Saionji family, who want Sōko dead, and the forces of the North House, who want her to conquer the world. For Sōko, the fight is not for power but for the right to choose her own humanity, even if it means sacrificing her life or accepting the love of the man sworn to end it.