Following the emotional aftermath of the Mugen Train incident, Tanjiro and his comrades recover at the Butterfly Mansion before embarking on a new mission. They accompany Tengen Uzui, the flamboyant Sound Hashira, to the Yoshiwara Entertainment District to locate his missing wives, who vanished while investigating rumors of demon activity.

To uncover the truth, the group must go undercover as women in the district's prominent houses. They soon discover that an Upper Rank demon, Daki, has been preying on the citizens for decades. The battle escalates into a brutal confrontation that requires the combined strength of the Demon Slayers and the awakening of Nezuko’s hidden powers to face not just one, but two lethal Upper Rank threats. This arc serves as a turning point, marking the first time in over a century that an Upper Rank demon has been successfully challenged.