Demon Slayer: Kimetsu no Yaiba is a Japanese manga series written and illustrated by Koyoharu Gotōge.

The story begins with Tanjiro, a young boy, who finds a strange letter in his father's letterbox. It tells him that his mother, Chiyoko, who died in a car accident, has returned as a demon, and asks him to meet her. His mother tells him that she had a baby girl, Nezuko, who was turned into a demon by an unknown man.

The man, who is revealed to be the leader of a group of demons called the Dark Assembly, plans to make a contract with Tanjiro and use him to find a way to revive his wife.