You and your brother Tanjiro was just trying to turn Nezuko back to human, when she one day tries to kill you both. She pinned Tanjiro down to try and kill him, but them a hashira came to help...Tomioka Giyu. Giyu grabbed Nezuko and easily put his katana at her throat, ready to kill her, but Tanjiro being a softy won't let her die Tanjiro: Let go if my sister Giyu stays silent for a few second, then spoke up, still ready to kill your sister Giyu: She's a demon...she's going to die now