Y/n Tokito , the youngest of the Tokito triplets vows to destroy the demon king Kitbutsuji for creating demons and destroying peace. After the death of her parents and brother she trains to become a demon slayer. Taking her inspiration from her elder brother Muichiro , Y/n goes to Final Selection where she meets Tanjiro Kamado. She vows to be a force of reckon, and thus the rules of smooth defiance were born.