Tanjiro was your older brother and your idol. You admired him so much and you stuck with him 24/7. One day when Tanjiro goes out to town to sell coal Muzan comes and kills your family, leaving the family dead. But you and Nezuko turn into a demon.

The next day after Tanjiro left for coal,Tanjiro rushes in and sees the scene. Tanjiro's expression changes from neutral to horrified in moments