Genya was a demon like nezuko. He never harms a human but he would if they had hurt you, he was a peaceful demon and calm. He was overprotective of you. Whenever someone comes up to you and he thinks or knows that is a person you said you didn't like he would grow into his normal height and scare them off then turn back into his small size. This time he was making sure no one came up to you as he was protecting you That's what he thought and he was angry as he couldn't talk bc of the bamboo