Tanjiro is brought before the Hashira and put on trial for traveling with his demon sister Nezuko. Tanjiro tries to explain his situation, but the Hashira do not accept it; All except for Giyu, who also broke the rules by protecting Nezuko. The Wind Hashira, Sanemi Shinazugawa, refutes Tanjiro the most and even harms Nezuko for being a Demon, stabbing her thrice through her wooden box.
The Master of the Mansion, Kagaya Ubuyashiki, arrives and asks the Hashira to pardon the Kamado siblings. A letter was sent from Sakonji (the ex Water Hashira), explaining the situation and asking for the Demon Slayer Corps to look past this, even saying that he and Giyu will also commit seppuku (retualized suicide) if Nezuko harms humans. While Mitsuri Kanroji (the Love Hashira) is very sympathetic to the siblings, Shinobu also expresses some sympathy and Muichiro Tokito (the Mist Hashira) is rather indifferent, the others still outright refuse to accept it and tell Kagaya so. Sanemi tries to prove Nezuko is an evil Demon by letting her out of thje box (and into an open room), then baiting her with his own blood. However, Nezuko refuses to take the bait despite her injuries and proves she won't harm humans.
Following the conclusion of the trial, Shinobu brings Tanjiro and Nezuko to the Butterfly Mansion, where Zenitsu and Inosuke are also healing their wounds. The Hashira commence their council with Master Kagaya ,while the other Demon Slayers heal. After their injuries are sufficiently healed, Tanjiro and the boys endure Rehabilitation Training under the tutelage of Aoi Kanzaki, one of the nurses in the Mansion, and Shinobu's apprentice Kanao Tsuyuri (the girl who pursued Nezuko and Tanjiro in Mount Natagumo).
Tanjiro also learns about Shinobu's past with a Demon who killed her sister. Tanjiro, Zenitsu, and Inosuke struggle with training at first, unable to beat Kanao in any form or capacity. Eventually, the boys regain their stamina and master Total Concentration: Constant, the ability to use the Breathing Technique all day and night long.
With their training complete, Tanjiro's group heads west to join the Flame Hashira, Kyojuro Rengoku, for the train mission. Meanwhile, Muzan dismantles the Lower Ranks and continues his schemes to crush the Demon Slayer Corps.