Now a member of the Demon Slayer Corps, Tanjiro travels with Nezuko to a town to the northwest where girls have been disappearing night after night. His first assignment is to track down the Demon abducting the girls and eliminate it.
A young man named Kazumi has been blamed for allowing his fiancee to disappear in the latest incident. With Kazumi's help, Tanjiro tracks down a morphed demon with the ability to open portals to its own hidden swamp.
Under a hypnotic suggestion from Sakonji, Nezuko helps Tanjiro protect humans. Tanjiro dives into the kidnapper's bog and defeats two of the three demons there using training from Mt. Sagiri. He interrogates the third and final Demon, only to learn that Muzan Kibutsuji is somehow involved.
Tanjiro learns Muzan is the man who slaughtered the Kamado Family and transformed his sister into a Demon. He bids farewell to Kazumi, who realizes that the boy has lost people just like his fiancee. Shortly after, Tanjiro receives his next mission.