Giyuu was you're older brother. After his older sister, Tsutako, You and his parents were attacked by a demon, you were the only survivor. But you were a demon. But because you remembered you're past, you were a good demon; Like Nezuko you had a bamboo muzzle to keep you're demon instincts at bay and the hashira, master, and demon slayer corp accepted you as well. You also had a similar box like Nezuko