Tanjiro is now clad in the uniform of the Demon Slayer Corps. His Nichirin Sword on his hip, and Nezuko, now awake, in a special box made by Urokodaki on his back, he heads out for his first assignment. A town to the northwest where girls have been vanishing nightly. There, Tanjiro meets Kazumi, haggard with worry after his girlfriend's been abducted. Though he does catch the scent of a demon nearby, there's just no demon in sight. Tanjiro is sure that a demon is behind this sinister incident...

The next mission is in Asakusa, Tokyo. Tanjiro is taken aback by the opulent Taisho Era cityscape, but soon picks up the demon’s scent there. His pursuit of the scent leads him to Muzan Kibutsuji. Tanjiro attempts to strike him down. But Kibutsuji transforms a passerby into demon, triggering a commotion. As Tanjiro desperately tries to get things under control, someone appears before him...

Tanjiro’s crisis continues. He uses multiple forms of the Water Breathing technique to hold out against Yahaba’s final Blood Demon Art, the "Kouketsu Arrow." Meanwhile, Nezuko and Susamaru are still battling it out. Worried about the outcome, Tamayo unleashes her own Blood Demon Art.

Seeing Tanjiro try to protect Nezuko even as he collapses triggers memories of Rui’s own past. Once a sickly boy, he became a demon after meeting Muzan Kibutsuji who gave him a share of his blood. But after he turns into a demon, his own parents try to kill him. Ever since then, he has been searching for a family. Seeking a bond that he can never hope to acquire...

Tanjiro's group, fresh from completing their training at the Butterfly Mansion, head to their next mission, the Mugen Train. There they rendezvous with Rengoku, who arrived ahead of them. Tanjiro is overwhelmed by the always-energetic Rengoku, Zenitsu is frightened by the prospect of facing demons as usual, and Inosuke is immensely excited by the sight of the huge machine. But on this train loaded with passengers, a new battle is about to begin.

Tanjiro, Nezuko, Zenitsu and Inosuke join Rengoku on the Mugen Train. Having heard that there may be demons on the train, they are on high alert, but they find themselves falling into a slumber. Within his dream, Tanjiro is reunited with his long lost family. However, it is soon revealed that this is a trap set by Enmu (Lower One).

Enraged by Daki's contempt for human life, Tanjiro attacks her with more intensity and gradually corners the demon. But he's already gone past his physical limit. As Tanjiro collapses and all seems lost again, Nezuko appears. A vicious battle ensues and Nezuko starts transforming into a more demon-like form...

Two simultaneous fights continue, Tanjiro, Nezuko and Genya against Hantengu and Tokito against Gyokko. Genya began to show a demonic form. Tanjiro asks him to look for Hantengu's real body, but memories of the past begin to plague Genya.