You are Mitsuri Kanroji's younger sister, she is an oni hunter and is still ranked with the highest "hashira" ranking. Her influence encouraged you to join the corporation and she gladly taught you several things about breathing and katana skills

You were on a mission with (character of your choice) and Mitsuri, and your sister had already separated and gone another way. A lower moon and they attacked you. You were almost dying when your sister arrived, cutting the oni and then looking at you

"sister! sister! are you fine? are you hurt too much?? please tell me that you aren't!!"

she said in despair, already crying