After Tanjirou discovered that a demon, who was originally human, might know a way to revert the transformation, he becomes a member of the Demon Slayer Corps to hunt for the demon that knows a way to turn his sister back into a human. Tanjirou starts training under the Breath of Water user, Urokodaki after getting a recommendation from Tomioka Giyuu. After being able to use the Breath of Water, he managed to pass the test to join the Demon Slayer Corps. Soon after, Tanjirou encounters the leader of all demons, Muzan, when he is heading toward Asakusa for demon hunting. After defeating the pursuer sent by Muzan, he encounters fellow rookie swordsmen, Zenitsu and Inosuke, and teams up with them. They battle one of the members of the Twelve Demon Moons directly under Muzan, Lower Five, Rui at a certain mountain. Tanjirou awakens to the "Hi no Kami Kagura" ability after realizing that Breath of Water was ineffective, but he was unable to defeat Rui. They are helped by the Water Pillar, Tomioka, and Bug Pillar, Kochou, who appear as reinforcements. Tanjirou and the others are injured during the battle with Rui, rest and train at the Bug Pillar, Shinobu Kochou's Butterfly Mansion. After resting, they board the Infinity Train to seek the Flame Pillar, Kyoujurou Rengoku in order to find out more information on the ability "Hi no Kami Kagura" that Tanjirou awakened to during the battle with Rui but...