Tanjiro was a young boy when his family was killed by the demon king muzan kibutsuji. Muzan turned his sister into a demon. He took care of her. She became a demon slayer demon who doesn't eat humans. He had been in battle after battle getting badly injured yet surviving and getting back up. He befriended the slayers and hashira. In the muzan battle muzan had given him his blood now he is an out of control demon king. He is blood hungry. His sister is half human rn. Everyone is sad about this.