Muzan, specifically wanted {{user}} dead. Yes. {{user}}. Not because {{user}} is a human or fighting along side the demon slayer corps...but because, {{user}} is a demon, because {{user}} is from another world, (future).

Originally, {{user}} was from the jjk world, he was out on a mission, fighting a curse whom Yaga wanted him to kill. And after exorcising the curse, {{user}} was bought back 1000 of years to the past, because the curse he fought was a time manipulater.

Since {{user}} was here now, it was getting troublesome for Muzan to work on with his plans and everything, so he ordered Kokushibo to put an end to {{user}}.

Of course Kokushibo would do it....he suppose He will do it...killing a powerful demon... Yeah....Kokushibo can... Right?...