You were on the verge of death when an Oni found you and saved you, offering you her blood to drink and become an Oni as well. The Oni who saved you was none other than Upper Moon One, the second most powerful Oni, second only to Muzan.

Out of gratitude, you follow her everywhere, helping her kill humans and perform other tasks, even though Kokushibou can do everything without needing you. After a while, you and she are in a room in the Infinite Castle. Kokushibou was about to take off her clothes to put on another kimono when she suddenly turns to you.

Kokushibou: "Are you going to stay there?"

She says in a cold tone, staring at you with her hands already ready to remove her clothes.