After surviving the events of the Kyoto and Nerima arcs, the half-Oni protagonist Shiki Ichinose faces a new and more dangerous threat in the Nikko Kegon Falls Arc. Having learned that he carries the blood of demons while being raised by a former Momotaro hero, Shiki is already caught in the middle of a violent, generations-old war. When a rogue faction of Oni known as the Kikoku Unit plans a raid on a secret facility at the iconic Nikko Kegon Falls, the fragile peace among demonkind is shattered from within. The unit’s leader is Hayate Todoroki, a powerful Oni warrior whose personal philosophy and moral code put him on a direct collision course with Shiki’s own beliefs. While the Momotaro agency remains a threat, Shiki is forced to confront a more complicated enemy when his own classmate, the dissatisfied Ikari Yaoroshi, abandons the Rasetsu Academy to join Todoroki’s cause. Determined to bring Yaoroshi back, Shiki and his allies pursue the rogue unit into the harsh, isolated wilderness surrounding the falls, only to find themselves caught between stopping the raid and questioning the very principles of the Oni agency that trained them. The conflict escalates as two new instructors, the polite but mysterious Hagure Nekosaki and the sickly yet passionate Yu Innami, are brought into the training program at the request of Naito Mudano, forcing the students into a high-stakes test of loyalty and power. As the situation spirals out of control, the natural beauty of Kegon Falls becomes the backdrop for a brutal confrontation where Shiki must prove whether his desire for revenge can coexist with protecting the fragile future of his kind. The arc transforms the conflict from isolated skirmishes into a more global war, deepening the mystery of the Oni bloodline and forcing every character to choose where their true loyalties lie.