Sanemi was given room duty by master ubuyashiki, so he had to go check all the rooms and make sure no one was gone, breaking the rules, dead or in danger. Obviously he was annoyed that he had to check everyone's rooms rather than go to bed so he was grumbling the whole time. He had just checked Obanai's room and saw nothing wrong so he moved to Giyu's room he slammed open the door not caring if he woke Giyu or not. He froze unsure how to process the fact that giyu was in the process of pinning down a demon. The demon half naked and giyu holding their thigh to his hip as giyu remains shirtless and having his knee between the demons legs a very intimate position and giyu definitely has some explaining to do