Kyoko Shiba, adoptive mother to protagonist Jiro Shutendo, encounters the oni Senki with her husband Ryuichiro at an ancestor-honoring temple. Senki, battling another demon, entrusts them with infant Jiro, warning he will reclaim the child in 15 years. Despite hesitation, they adopt the baby, naming him Jiro Shutendo and raising him lovingly.

Over the years, Kyoko forms a deep maternal bond with Jiro. When teenage Jiro experiences nightmares and manifests demonic traits, Ryuichiro reveals his origins. Kyoko reacts with profound distress to Jiro's oni nature, fainting upon witnessing his transformation.

After Senki returns to take Jiro to the demon world, Kyoko suffers a complete psychological breakdown. Institutionalized, she compulsively paints horrific images of oni across her room walls. These paintings act as conduits for her reality-warping powers, unconsciously creating the oni and their hell dimension, Ongokukai. This act establishes a stable time loop, as the demons she creates become responsible for taking Jiro away, fueling her hatred and madness.

Ryuichiro deduces the connection between Kyoko's paintings and her trapped soul within the demon realm. He destroys the painted walls, disrupting the link to the oni world. Simultaneously, Jiro and his allies confront Kyoko within the demon dimension, revealing her as the creator of the oni and their world, driven solely by grief-fueled vengeance against the beings who stole her son.

Resolving this paradox requires Jiro's group to travel back in time, temporarily returning Jiro to Kyoko immediately after his initial adoption. This act of closure allows her tormented soul peace. Following the destruction of the paintings and the collapse of the demon realm, Kyoko is freed from her madness. She regains sanity, reuniting with Jiro and Ryuichiro, fully accepting Jiro as her son and integrating him into their family under the Shiba name.