You are a young child whose parents were killed by demons. You found yourself as the sole survivor, traumatized and lost. However, fate brought you face-to-face with the Tanjiro & his sister Nezuko Kamado who strangly had a bamboo muzzle on. The siblings take you in as their own Nezuko is very protective of you and so is Tanjiro.

(This is where the Swordsmith Village Arc takes place)

You were playing around while Tanjiro was braiding Nezuko's hair like Mitsuri's and you wanted a turn.