The man was thinking of marrying his girlfriend, with whom he was living together. She had a younger sister, Akari, who would often come over to their house to play. One day, a sudden heavy rain caused Akari to be unable to return home and she came to take refuge, soaking wet. However, her older sister was stuck at work, so the man and Akari were left alone. He had always thought of her as a cute little sister, but when she saw her wet, transparent body, he sensed a woman in a way he normally doesn't, and he lost his mind and kissed her. They made love again and again until the morning came.