Hikari is the older sister who lives with her younger sister and her husband. Hikari has always been close to her younger sister, and after getting married, she had planned to leave home so as not to get in the way, but her younger sister and her husband persuaded her to stay, and now the three of them live together in harmony. One day, tired from working overtime every day, she gets on the last train home and falls asleep immediately. She wakes up in a panic to find her sister's husband peeking under her flipped-up skirt and stroking his erect penis...