Season 3 - Episode Guide

After their battle with the Upper Rank Six siblings, Tanjiro, Zenitsu, Inosuke, and Nezuko are found by the Kakushi. In the Infinity Castle, Muzan Kibutsujisummons the remaining five Upper Rank demons – Akaza, Upper Five Gyokko, Upper Four Hantengu, Upper Two Doma and Upper One Kokushibo. He admonishes them for their failure to kill the Ubuyashikis and find the Blue Spider Lily. When Gyokko provides new information, he is sent on a joint mission with Hantengu. While Zenitsu and Inosuke are summoned to individual missions, Tanjiro continues his rehabilitation. When his swordsmith Hotaru Haganezuka refuses to forge him a new sword, Tanjiro is told to meet him at the Swordsmith Village to discuss the matter in person. He arrives with Nezuko and meets the village's chief, Tecchin Tecchikawahara, who reassures Tanjiro he will bring Hotaru back to build the sword. Tanjiro is later shown to the village's hot springs where he meets the Love Hashira Mitsuri Kanroji, who is initially dejected after being ignored by an unknown person. While in the hot springs, Tanjiro encounters Genya, the Wind Hashira Sanemi Shinazugawa's younger brother and fellow Demon Slayer, who refuses Tanjiro's hospitality and storms off. At the village, Mitsuri hints at Tanjiro about a "secret weapon" hidden somewhere that can make him stronger and bids farewell to the siblings. The next day, while searching for the weapon, Tanjiro finds the Mist Hashira Muichiro Tokito in an argument with someone and sees that seemingly with them is a man from his dreams.

While eavesdropping, Tanjiro watches as Muichiro threatens the swordsmith he was arguing with. He tries to defend him but the indifferent Hashira knocks him out for interfering. After waking up, the boy, named Kotetsu, explains that the "man" he saw is actually an advanced mechanical training doll, built after a swordsman who lived over 300 years ago. He explains the doll was made by his ancestors, and as he lacks a family, it is all he has to pass on to the next generation. Tanjiro agrees to protect it, but Muichiro appears, having finished his training session and causing extensive damage. However, after Kotetsu discovers it is still functional, he tells Tanjiro to train with it in order to become stronger than the arrogant Muichiro. However, training proves harsh as Kotetsu denies Tanjiro food and water when he fails to connect hits on the doll. When Tanjiro eventually faints from exhaustion, he imagines himself in the afterlife and sees a peculiar stone in the Sanzu River, enabling him to detect a scent faster than the Opening Thread. He uses this to his advantage, eventually landing a powerful strike on the doll's head, which shatters and reveals a concealed sword inside.

Tanjiro becomes disappointed after he discovers the sword rusted. However, a swole Hagenazuka appears, revealing he trained in solitude to be able to forge a better sword for Tanjiro. As such, he offers to restore the rusty sword, giving Tanjiro another one in the meantime. That night, while trying to befriend Genya, swordsmith Kanamori is brutally devoured by Gyokko who, alongside Hantengu, has found the village. After Muichiro is moved by Tanjiro's sense of kindness towards others, Hantengu enters their room, only to be quickly beheaded. However, two individual demons regenerate from the severed body parts, each with different, powerful abilities. After one of them blasts Muichiro far away, the other nearly electrocutes Tanjiro with a staff, before Genya appears and beheads them both with a sawed-off shotgun and a Nichirin knife. However, Hantengu again duplicates, and one of the demons deafens Tanjiro with a sonic attack while Nezuko tries to defend Genya. Meanwhile, Muichiro runs back to assist, but finds Kotetsu in peril from one of Gyokko's spawn. Initially electing not to help him, he saves him just before being eaten after remembering about the importance of kindness with others.