The latest installment in the "Documentary: Close-Up Sex" series delves into the forbidden relationship between a sister and her brother-in-law. This time, it's the story of a younger sister who falls head over heels for her brother-in-law at first sight. They meet after their parents remarry, but since the brother-in-law lives alone, their chances to see each other are limited. As time passes, the sister becomes a university student. While busy with job hunting, she visits Tokyo frequently and uses these opportunities to stop by her brother-in-law's place. Each time, she showers him with adorable, flirtatious advances. What will become of their relationship? Forbidden feelings begin to stir, driving the story into deeper, more intense territory.