Tanjiro Kamado and his sister Nezuko Kamado are introduced as the main protagonists of the series. The Kamado Family is slaughtered by Demons and Nezuko is transformed into one. These chain of events thurst Tanjiro into his journey to avenge his family and restore his sister's human form.
In order to carry out his mission, Tanjiro must become a Demon Slayer. Giyu Tomioka sends the Kamado siblings to stay with his teacher, Sakonji Urokodaki. Sakonji takes them in and trains Tanjiro to become a swordsman. Nezuko falls into a deep sleep during the two years it takes Tanjiro to master Water Breathing.
During his training, Tanjiro meets two spirits of Sakonji's former students. They train Tanjiro and give him the strength of all of Sakonji's fallen children. This allows Tanjiro to qualify for the Demon Slayer CorpsFinal Selection.
On Mt. Fujikasane, where Final Selection is held, a Demon lives that has slain thirteen of Sakonji's students. Makomo and Sabito believe that Tanjiro can be the one to avenge all Sakonji's children. Tanjiro crosses paths with the demon and struggles to best its power. However, with the guidance of souls closest to his heart, Tanjiro bests the monster.
Tanjiro and four other students are the only ones to survive seven days in Final Selection. They are marked with the lowest rank of Demon Slayer and each of them picks a Nichirin Blade ore. Tanjiro returns to Sakonji's house to find Nezuko has awoken. She embraces him and they reunite after years along with Sakonji, who's grateful to find one of his children has survived. Days later, Tanjiro's blade is delivered to him by a swordsmith, and proceeds to turn black when he holds it. He receives orders for his first mission soon after.