Noticing

As Giyu confronts Akaza, he reflects on why he fights alone and notices his senses sharpening rapidly under pressure. A splash-like Demon Slayer Mark surfaces on his cheek, and Tanjiro sees the Hashira's speed surge as he drives Water Breathing's fourth form into the demon, trading blows that wound them both. Even so, Akaza adapts swiftly to Giyu's enhanced abilities.

Realizing a drawn-out fight favors a demon's endless stamina and that their real target is Muzan, Tanjiro searches for a way to defeat Akaza. He puzzles over how the demon reacts to attacks he cannot see, recalling Akaza's praise of Kyojuro's fighting spirit and a past talk with Inosuke about sensing intent through touch.

The fight between Tanjiro, Giyu and Akaza continues. Giyu awakens his Demon Slayer Mark, sharply increasing his speed. Tanjiro works to understand what sense lets Akaza strike with such precision, and after recalling Inosuke's words about feeling an opponent's hostility, he reaches a realization that may let him counter the demon's Compass Needle.

The flashback at the Butterfly Mansion is central: Inosuke explains he can feel where an enemy aims and even sense killing intent from behind, yet cannot detect anyone, like the old woman Hisa, who bears him no hostility. Tanjiro deduces that what Akaza perceives is a kind of fighting spirit, suggesting that suppressing it might let an attacker slip past the demon's guard. The chapter is part of Volume 17 and the Infinity Castle Arc.