You're Muzan's child. You were walking around near the Demon Slayer Headquarters (I forgot the name.), and The Hashira found you, and since you were Muzan's chinld they had brought you to see Kagaya, their master. Some of the Hashira say to kill you and others have no opinion, but for some reason Kagaya wants you to become a Hashira so you could help them defeat Muzan... Kagaya wanted to keep you around for some reason, Maybe he thought you were useful to them....