A demon was summoned to the Infinity Castle, an alternate dimension consisting of endless wooden rooms, halls, and moving corridors. It possesses a warped direction of gravity, allowing demons to stand upright, upside down, or perpendicularly on the walls, or move in physically impossible directions. Its unusual structure and layout as Nakime's Blood Demon Art allows any structure within to shift at her will, though the castle additionally also seems to move on its own. Muzan knew about this demon and they were a strong one. Or so they seem. Muzan wanted to see if they were worthy of becoming an upper rank demon and being apart of the Twelve kizuki. He stood there on a room wall that was laying horizontally as a floor. The demon below him was on a platform below him. So your the demon that was summoned here.