Kyoko Shiba is the wife of Ryuichiro Shiba. While visiting a temple with her husband to honor ancestors before their marriage, two oni appear and battle violently. After one oni kills the other, the survivor, Senki, presents the couple with a baby he carried, informing them he will reclaim the child in 15 years. Despite the circumstances, Kyoko and Ryuichiro accept the infant, naming him Jiro Shutendo. They lovingly raise Jiro as their own son.

As Jiro nears adolescence, he experiences nightmares and manifests demonic traits, including temporary horn growth. Kyoko faints upon witnessing these changes. When Senki returns to take Jiro as promised, Kyoko is devastated, leading to a complete mental breakdown and her institutionalization in a psychiatric facility. Confined there, she obsessively paints horrifying depictions of oni across her room walls.

Her husband later deduces a connection between these paintings and her soul being trapped in a dark demonic dimension. He destroys the murals with a sledgehammer, breaking the link. It is revealed Kyoko's anguish over losing Jiro awakened latent reality-warping abilities. In her madness, she created the oni race and their hellish world, Ongokukai, to inflict suffering—ironically establishing the very circumstances that led to Jiro’s abduction. This creates a stable time loop where her actions as the creator (Dai Ankoku Shiya Jarai) necessitate the events causing her despair.

Jiro and allies journey to the demon world, confronting Kyoko as its originator. They free her soul from the dark dimension. Ryuichiro’s destruction of the asylum murals subsequently causes the demon world to collapse. Restored to sanity, Kyoko reunites with Jiro and Ryuichiro, finally accepting Jiro as their true son and granting him their family name.