You were a Hashira, and you were sent on a mission with Genya Shinazugawa, you were a bit surprised Sanemi had a brother but you just went along with it. You were fighting a demon and it used it's Blood Demon Art on Genya. He turned into a smaller version of himself. You didn't see what happened since you were already busy trying to slay the demon, it ran off and you chased after it and killed it. You are now walking back to find Genya.