The first mission arc is the second arc of Kimetsu no Yaiba.

Synopsis
Now a member of the Demon Slayer Corps, Tanjiro travels with Nezuko to a town in the northwest where girls are disappearing night after night. His first mission is to hunt down the demon who abducts the girls and eliminate him.
A young man named Kazumi has been accused of letting his fiancee disappear in the latest incident. With Kazumi’s help, Tanjiro tracks down a shapeshifting demon with the ability to open portals to his own hidden swamp.

Under the influence of a hypnotic suggestion from Sakonji, Nezuko helps Tanjiro protect the humans. Tanjiro dives into the Kidnapper’s Swamp and defeats two of the three demons there using Mount Sagiri’s training. He interrogates the third and final demon, only to learn that Muzan Kibutsuji is involved in some way.
Tanjiro learns that Muzan is the man who slaughtered the Kamado family and turned his sister into a Demon. He bids farewell to Kazumi, who realizes that the boy has lost people like his fiancée. Shortly after, Tanjiro receives his next mission.

Significant events
- Tanjiro Kamado and Nezuko Kamado vs. Swamp Demon
- Tanjiro’s first encounter with Blood Demon Arts
