During summer break while their parents were away, the birthday present he received from his older brother was a sexual encounter with his brother's regular girlfriend, the gyaru Arisu. Losing his virginity to her, he was taught step by step how to make her squirt. Despite having zero prior knowledge about sex, he quickly mastered the technique to make her climax with every session. As his skills improved, Arisu's heart and body gradually became drawn to him, evolving their relationship into one where they passionately desired each other like lovers.