Shortly after marrying, Yasuko maintains a harmonious relationship with her husband, but remains somewhat distant from her stepson, Takayuki, a ronin preparing for college entrance exams. One day, she catches him sleeping with his penis exposed, and she trembles with uncontrollable excitement. Overcome by prolonged abstinence and mounting sexual frustration, she reaches out and touches his erect cock, causing him to ejaculate instantly. However, his insatiable, highly potent penis isn't satisfied with just one release, quickly becoming rock-hard again. Mesmerized by his relentless arousal, Yasuko senses a new shift beginning in their relationship.