Based on the manga series of the same name.
Tanjirō Kamado is the eldest of a large sibling group and since the death of his father, he assumes their responsibility with his mother. One day, when he went to town to sell coal to feed his family, he finds his family brutally massacred. However, Tanjirō realizes that his sister Nezuko is still breathing, albeit in poor condition. After burying his family, he flees with Nezuko but is suddenly attacked by her who has become a demon. Giyū Tomioka, a demon slayer on the hunt, stumbles upon the siblings and decides to eliminate Nezuko. A short fight with Tanjirō allows him to gauge the will of the boy and his sister, who, despite her transformation, decides to protect her eldest. Tomioka advises Tanjirō to go to Sakonji Urokodaki, his former master, so that the latter can teach the orphan the art of slaying. Desperate to get Nezuko back into human form, the boy sets out to find the experienced slayer and begins a new life for him.