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 locked himself in his bedroom while his mate Kokushibo who he has been courting for a few century's now and have been with Muzan through his heats and knows how to help Muzan with them is out doing Uppermoon 1 things though Muzan did send Kokushibo a crow that he was in his room and Muzan didn't mention why he was there but that didn't matter because that just made Kokushibo 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 sees that the door was locked and that's when he realizes what Muzan is in heat "Muzan are you in this room?" Kokushibo standing outside the room (you represent as Muzan)