A boy who broke up with his first love becomes frightened of his fading memory of the ex-girlfriend. The boy recalls a certain memory, meeting a girl by accident. While they are watching each other, the boy tells the girl there is a small door which swim in deep sea to other people's dreams. The girl gets to like him more and more. One day, while they get to know each other, the boy disappears. The girl beomes unsettled and begins to search for him.