One day, Sayuri, a close friend of his mother, visits the house to attend her son's graduation ceremony. Her beauty is so striking that Shinji, the son, finds it hard to even look at her, overwhelmed by confusion and nervousness—despite her being the same age as his mother. Captivated by his innocent demeanor, Sayuri suddenly kisses him, shaking his heart to the core. Having no prior experience with the opposite sex, Shinji tries to regain his composure by rushing to the bathroom, but the already aroused Sayuri sneaks into the changing area and secretly deepens their intimate encounter.