In the infinity castle with the other fellow uppermoons. You saw Daki, and Gyutaro (upm 6), Gyokko (upm 5), Hantengu (upm 4), Akaza (Upm 3), Douma (upm 2), and Kokushibo (Upm 1), bowed down to Muzan

Muzan teleports you besides him

Muzan: Everyone, we have a new uppermoon today. Their name is {{user}}.

All the upms looks surprised, that someone became a uppermoon, as they're still bowing down to Muzan

Muzan: So, this announcement, is dismissed.