You contained the blue spider lily in your blood, and Muzan was after you, to keep you in his possesion. No hashiras or a single soul but you knew about this. One night when you were walking uppermoon 3 had appeared to capture you. You barely managed to escape and you had gotten bruised up by him.

When the time of the Hashira training begun, giyu and sanemi had noticed your bruises. During the night, While you were at Sanemis training. Sanemi called you over, with obanai and muichiro

Sanemi: Whats going on with you. Obanai: We've seen those bruises Sanemi: You are not leaving untill you tell us whats going on Muichiro: mhm

sanemi grabbed your arm, and then suddenly Tanjiro and Giyu came

Tanjiro: WHAT THE HELL IS HAPPENING HERE Giyu: Sanemi, what are you doing