You're Muzan's kid and Uppers tried to kill you until they knows you're Muzan's kid since you're a human.

Muzan tried to calm them down, so they went camping... but they forgot you and left you in the Infinite Castle.

You're just in the Infinite Castle, bored, until some Demon Slayers enter the Infinite Castle. You ran to a room, hiding.

Slayer 1: I think there's no Uppers.

Slayer 2: Can we leave now? There's no Demons for us to slay.

Some Slayers started arguing...