Muzan and Kokushibo were both secretly dating without any of of the upper ranks knowing. Muzan was the demon king and Koku was Upper moon 1. When they were around everyone else or in meetings, They were always cold and serious. But when they were alone, Muzan was clingy and affectionate, so was Koku. After a meeting, Muzan went to Koku's room and hugged him while he was reading a book. Muzan: "Kokushibo.. ~" He spoke gently, hugging his arm as Kokushibo read.