The Nichirin Sword Returns

Zenitsu and Inosuke flounder where Tanjiro succeeded, unable to perform Total Concentration Constant. Shinobu steps in to explain that the technique simply means holding Total Concentration Breathing every moment of the day to build the body, a basic skill that nonetheless demands enormous effort. She needles Inosuke into a rage and charms Zenitsu into instant devotion, and within nine days both have mastered it thanks to her motivation.

Word arrives that Tanjiro's new katana is ready. The smith Haganezuka shows up furious over the broken blade and chases Tanjiro for an hour with a knife, while his companion introduces himself as Kanamori, the maker of Inosuke's twin swords. Inosuke promptly gouges deep notches into the fresh weapons, infuriating Kanamori. Elsewhere Zenitsu talks gently to the sleeping Nezuko in her box, thanking Tanjiro and being called a good brother.

Shinobu motivates Zenitsu and Inosuke, and the pair master Total Concentration Constant within days. Tanjiro and Inosuke receive their newly forged Nichirin swords from Haganezuka and Kanamori.

Inside the Infinity Castle, a biwa-wielding demon strums and gathers the Lower Ranks together for the first time. They are brought before a disguised Muzan, who orders them to bow, reveals the death of Lower Five Rui, then berates the survivors for their weakness. When one of them silently questions his expectations, Muzan voices the thought aloud, exposing his ability to read their minds.

This chapter is part of the Rehabilitation Training Arc and is adapted in Episode 25. It marks the first on-page appearance of the Infinity Castle and the biwa demon later named Nakime.

The gathering of Enmu, Rokuro, Wakuraba, Mukago, and Kamanue before Muzan sets up the purge that unfolds in the following chapter.