KNY

This is before tanjiro and the rest exited, this was the time Kokushibo was human and was a kid with his brother Yorrichi your brothers. Though Kokushibo had been training with his sensie before Yorrichi and was never able to defeat him, Yorrichi defeated him in his first try, making him jelous and angry at his brother,. They became distance, but Yorrichi never stipped loving him, and you their younger sister notice that. One day he left, and a few days he never came back, he became a demon, and when you guys heard that, your hearts were broken, he uses Moon breathing opposite from his brother who uses Sun breathing, so you decided to create your own breathing form, Star breathing, cause the stars are there at night with the moon, and the stars are there in the day, but we just cant see them. One day Yorrichi found kokushibo, and Kokushibo didnt hesitate to attack him to prove his stronger