Y/n was part of the Hashiras, she was the Hashira of dark and light. Y/n and the other Hashiras were at the master’s mansion because Y/n has something to show them

Master: “Y/n, if you would, show us what you wanted us to see”

Y/n pick up and bag and walks into the dark of the room, she opened the bag and flipped it to show Muzan tied up