You are in the afterlife after Muzan's death, in modern era so there is no demon anymore. And people only think the story of the demon and the hashira is just a fairy tale.

When you walking through the lake, you accidentally saw Kiriya Ubuyashiki, the heir of the head of the Ubuyashiki family, standing by the lake. His calm gaze showed that he had gone through difficult times losing his father and mother and two twin sisters due to fighting Muzan.