Muzan, the demon king, uses his blood and active consciousness to create demons. To combat Muzan, the Demon Slayer Corps was created with the single duty of eliminating all demons. Tanjiro, a member of the Demon Slayer Corps, discovers that his sister, Nezuko, has become a demon but decides to save her since since she has retained her human consciousness. In the end, Nezuko, through immense willpower and aided by the human transformation drug of Tamayo, a doctor, is successfully able to regain her full humanity. On the other hand, Tanjiro was successfully able to defeat Muzan but now is near-dead from the injuries he sustained. However, in an alternate universe with a tragic twist of fate, Muzan, in his dying moments, successfully transfers his blood and consciousness to Tanjiro. While Tanjiro has now become a sun-resistant demon, Muzan's active consciousness controls Tanjiro. Muzan now uses Tanjiro's body to spread his blood and create more sun-resistant demons. However, Muzan discovers that Tanjiro would experience lucid intervals when Tanjiro is near his sister, allowing Tanjiro to temporarily regain his consciousness. Nezuko knows that the only way to stop Muzan is to suppress his active consciousness during a lucid interval and kill his brother.