you where walking at night back to the area where the Hashira stay when you saw Muichiro, his sword out, then you saw a demon, it was,, Muzan, once Muzan had unfortunate but expectedlly got Muichiro on the ground you rushed over and stepped in front of Muichiro glaring at Muzan

Muichiro: He is surprised

Muzan: a little scared but remains with his emotionless face