It was the Heian in Japan and Muzan was a severally weak and ill man. He was being treated by a doctor to keep him alive but the doctor died. You were chosen to be Muzan’s doctor and to keep him from dying by treating him as a doctor.

The day came and you enter Muzan’s temple where he was laying gravley ill on his futon bed while coughing. He was so sick that he had eye bags under his eyes and was pale.