An Upper Rank Demon has been defeated for the first time in a hundred years by Uzui, Tanjiro, and his comrades' effort. This news causes a ripple effect not only among the members of the Demon Slayer Corps but also the Upper Rank demons who have been summoned by Muzan Kibutsuji. Meanwhile, Tanjiro is recovering at the Butterfly Mansion when he discovers that he has upset his swordsmith Haganezuka after chipping his sword and decides to head to the village where the swordsmiths live to talk to him in person.

Tanjiro encounters Mist Hashira Muichiro Tokito and Kotetsu, a boy from the village, arguing. Muichiro demands that a "certain key" be handed over to him from Kotetsu. Being unable to look on in silence, Tanjiro intervenes to speak on behalf of Kotetsu. However, Muichiro refuses to listen. According to Kotetsu, the key is used to operate a battle-type mechanical doll, Yoriichi Type Zero, that mimics the movement of a certain real-life swordsman...

Yoriichi Type Zero is destroyed at the end of Tanjiro's training, but a sword from over 300 years ago appears from inside. Kotetsu gives Tanjiro the sword. However, it is badly rusted. At that moment, Haganezuka appears and takes the sword with him to perform a grueling whetting process handed down within his family line. Meanwhile, the presence of demons is inching closer to the village...

Muichiro rescues Kotetsu, who was being attacked by a goldfish demon. He tries to rush to the village where crisis is looming, however, he is asked by Kotetsu to rescue Haganezuka and Kanamori, so he begins heading their way instead. Meanwhile, Tanjiro, Nezuko, and Genya are facing off against the demons who have split into four separate bodies. Separated from the rest, Tanjiro alone continues to fight a close battle with the demon with a mark of the word "Joy"...

Upon arriving at the village, Mitsuri rushes to the chief of the village, Tecchin, and finds that all of his guards have been defeated, and he himself is in a life-or-death situation. Muichiro is being guided by Kanamori, whom he rescued along the way, to the studio to receive his sword. However, Upper Five Gyokko is waiting in front of the studio, where Haganezuka is also working...

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.

Genya aims for the neck of the fifth demon, but the sword breaks due to the unexpected hardness of the neck, and the gun doesn't work either, and he is cornered. He entrusts Tanjiro with the task of confronting the fifth demon, which is believed to be Hantengu's real self, as he cannot cut his neck with his own strength. Receiving Genya's feelings, Tanjiro swings his sword at the fleeing demon.

Muichiro, with the help of air blown by Kotetsu to him, escapes Gyokko's Water Prison Pot. Muichiro finally recalls his tragic past.

Armed with his memories, Muichiro feels powerful and invincible, convinced that the demonic fifth moon has no chance against him.

Tanjiro, Nezuko, and Genya are struggling through an arduous battle against Zohakuten and his five tree dragons. They are forced to fight defensively against the tree dragons using the four emotion demons' powers, and Tanjiro is swallowed by one of them amidst the fight. Just as Tanjiro is close to meeting his demise, Mitsuri arrives in the nick of time and rescues him. And now, Mitsuri faces off against Zohakuten to rescue the captured Nezuko and Genya!

Tanjiro continues the fight against Hantengu. Amidst all his injuries and the Upper Four's skill, will he be able to defeat him? As the battle draws to a close, the Demon Slayer squad must race against time to end the fight before dawn.