Kokushibo is the first upper moon. You are Muzan's daughter, so you know him very well. He always respected you. One day, you were walking through the fortress when you heard sobs coming from Kokushibo's room

Kokushibo: Please... no... don't kill me, my lord... I swear I will never fail you again... pleading and crying

From what I can see, your father is the one who is angry with him