Kozuka Knives Arc

Running across volumes 20 to 22 and chapters 166 to 191, this is the manga's tenth arc and the first of the Ultimate Yokai Saga, following the Danmara Arc and leading into the Typhoon Human Arc. Reduced to a tiny size after fleeing Danmara, Momo leans on Okarun and the school's History and Culture Research Club to find a way back to normal. Their research is interrupted when a knife-bearing student, Koki Yukishiro, commanding an army of tiny creatures, attacks her. The club soon discovers Koki is a blackmailed pawn, one of several knife wielders serving a shadowy mastermind who gathers powers from victims and ultimately covets Momo's own.

Attending school in secret, the shrunken Momo is hunted through the library by Koki Yukishiro, a girl wielding an Asura knife and a swarm of invisible pygmies. The club corners her, only to be lured into Empty Space, where the pygmies stitch their clothes down and pelt them with blades and flame. Momo pinpoints Koki and breaks her concealment, and after Queen intervenes the truth spills out: a teacher blackmailed Koki into stealing Momo's power, threatening to expose her secret account. Koki cannot recall the teacher's face, a sign the Orchestrator scrubs the memories of his agents.

Meanwhile, Seiko visits the cursed-object collector Payase and his associate Kashimoto, learning the Uchide-no-Kozuchi enshrined at Izumo Taisha could undo Momo's shrinking. The meeting is ambushed by jiangshi and the iron-bodied Minotaur, an agent who grows tougher with every blow. With Payase's shadow powers and Kashimoto's absolute-zero Ice Flame, Seiko shatters him, exposing a desperate human beneath who confesses he chased a wish to save his dying wife. He reveals the knives come from the stolen sword Asura and that the Orchestrator messages many agents at once.

Fitting Koki with a nanoskin camera, the club tails her to flush out the blackmailer. The hunt drags Aira into a gym haunted by the Severed Head Dribblers, where she rescues a decapitated Rin and Koki, restores them beneath the hoop, and learns the teacher Murakami is the extortionist. Koki's revived piano playing amplifies Rin's gravity power and triggers her own Lord of the Flies ability, swarming Murakami with flies. The agent Adachi then steals Murakami's power with an Asura knife, only to learn from the Orchestrator that he too was a subordinate, not a target.

Outside, Okarun and Kinta face Hase, now armed with Jumping Crone powers, and the surviving Kur exosuit alien. Stripped of Turbo Granny's strength but physically superhuman, Okarun fuses with Kinta's nanoskin into a clumsy two-man robot and finally downs Hase. Vega disrupts the Orchestrator's agent as he tries to seize Adachi's loot, recoiling at the Fairy-Tale Card emerging from the man's back. As the arc closes, Seiko leads the Family and the cursed Unji and Daiki toward Shimane, while Momo, fading further, struggles to make Bamora even notice her.

The arc confirms the kozuka knives forged from the Asura let a ring of Power Collectors steal and bestow abilities for the Orchestrator, who dangles wishes before any agent amassing enough yokai powers and blasts a shared alert whenever a target is named. Koki debuts and keeps her Lord of the Flies power, the pygmies are revealed as forgotten outcasts drawn to the lonely, and Queen returns as a spirit-sensitive nurse tied to Manjiro. Payase and Kashimoto enter as cursed-object experts, and Seiko learns the Uchide-no-Kozuchi can restore Momo. Hase returns as a rival turned power thief, Adachi works for the Orchestrator to fund her mother's care, and the freed Jet Booster exosuit alien, now serving Saint-Germain, allies with Hase against Okarun. Unji and Raiya reappear seeking a cure for Daiki's runaway aging, and the Family departs for Shimane to lift Momo's curse under the supermoon.