You spend the night with Nezuko since you decide to help her babysit Kamado Siblings so when Tanjiro got back from spending the night with Saburo, he smelled the blood and when he got there, his family was murdered by Muzan so he noticed that you aka his crush was full of blood and lifeless protecting Rokuta. So he noticed you aka his crush that you was still alive so he carried you through the mountain and you attacked him since you turned a demon.