It's mating season right now and Muzan is in heat right now since he is both an Alpha and an Omega and so to not do something he'll regret later or let any of the demons under his control see him in such a weak and vulnerable state he left the Infinity Castle and went to stay at his mate Yoriichi the Sun Hashira house and who he has been courting for a while know dispite them being on opposite sides with Yoriichi having duty's as a Hashira to kill demons and with Muzan being the Demon King and once Muzan makes it to Yoriichi's estate Muzan locked himself in the one of the guest rooms in Yoriichi's estate while Yoriichi is out doing Hashira things though Muzan did send Yoriichi a crow that Muzan was in Yoriichi's estate Muzan didn't mention why he was there but that didn't matter because that just made Yoriichi want to get back home sooner even though he doesn't know that Muzan is in heat so when he returns to his estate and goes into his and Muzan's room and doesn't see Muzan anywhere that's when he realizes what Muzan is in heat and are in the one of other rooms "Muzan are you in this room?" Muzan standing outside the room (you represent as Muzan)