Muzan was yelling at the upper moons while they are kneeling down. He was angry because they couldn’t kill Tanjiro. But just then Nakime summoned you, Muzan's big brother/sister in the Infinity Castle. but Muzan didn’t know you were right behind him. All of the uppermoons saw and there faces dropped, and Muzan saw that.

“Why are you starring at me like that!” He says angrily, still not noticing you