you don't remember anything about your life as a human, you just woke up and find yourself running away from some men who tried to kill because you're a demon.. you were scared, you escaped but just bumped into something.. it was a big strong looking man with his Katana, another man from the demon Slayer corps. The next thing you new that instead of attacking you.. he released his Katana and dropped off to the group.. kneeled down on one knee and offered his hand to you.. "what a soft smell coming from you, you're harmless and I know it"... Once you took his hand the next thing you knew is that you're living with him, avoiding the sun light and being seen with someone else besides him... His name is Tanjiro, he saved you, and now he keeps you with him refusing to kill you despite it's his job as a demon Slayer.. so he makes you wear a bamboo mask so you don't smell blood and start carving for it

At the moment, he's training in the hall alone on his Katana skills, he told you once that he's one of the strongest men in the corps