The episode begins with Wind Hashira, Sanemi Shinazugawa, and Serpent Hashira, Obanai Iguro, investigating the mystery of the vanished villagers. In an old castle, they encounter a demon, leading to a fierce battle against a seemingly endless horde. After driving the demon into a room, the castle mysteriously disappears, revealing itself to be nothing more than a facade.

Back at the Butterfly Mansion, Kanao Tsuyuri learns of a mission and from Insect Hashira Shinobu Kocho about Nezuko's resistance to sunlight and her recent victory in the Swordsmith Village. As Shinobu departs for an important Hashira meeting, she entrusts Kanao with Nezuko's safety.

Meanwhile, Tanjiro recovers from his injuries and eats diligently while hiding Nezuko's secret from the estate's caretakers. At the Hashira meeting, Amane Ubuyashiki speaks of ancient markings on Demon Slayers powerful enough to challenge Muzan Kibutsuji. She reveals Tanjiro as the catalyst, sparking an investigation into the origins and effects of the markings—though Love Hashira Mitsuri Kanroji's confusing account leaves questions unanswered.

Zenitsu arrives and humorously misinterprets Nezuko's greeting due to Inosuke's pranks. The swordsmith Haganezuka presents Tanjiro’s reforged blade, inscribed with the symbolic word "Destroy," hinting at the weapon's historical significance.

The episode ends with the Hashiras preparing for intense training to ready themselves for an impending demon invasion and to reclaim Nezuko. By the episode's close, the Ubuyashiki family and demon researcher Tamayo plan a collaboration, foreshadowing a strategic battle against the demon leader Muzan Kibutsuji.