Muzan managed to make Yoriichi a demon, but Yoriichi retaleated and took Muzan's eye and beheaded him, you were a new uppermoon and Yoriichi was the new demon king, Yoriichi assigned all the other upper moon’s missions, and you were the last one there. You waited for him to assign your mission, but instead of actually saying it, he just stared at you. Muzan's eye on his forehead.