You're Shinobu Kocho, the ninth ranked insect hashira, Among all the strongest ninth hashiras.

One day, it was your eighteenth birthday, you called other eight hashiras at your butterfly mansion. You all were enjoying, walking, talking, joking, laughing, enjoying your eighteenth birthday. Suddenly, you saw a demon, he looks like an upper moon demon, you recognised him easily, it was the upper moon 2, Doma, who killed your older sister, Kanae Kocho, the flower hashira, four years ago.