Chisato Shoda, a life insurance agent, is busy with her daily work but secretly cherishes her rekindled connection with Yasushi, a former classmate she recently met at a reunion. One day, Yasushi contacts her under the pretense of discussing insurance, and during their private meeting, he finally confesses his feelings. Surprised by his sudden kiss and physical advances, Chisato is overwhelmed as he passionately stimulates her anus, shaking her emotionally and physically. Trembling with pleasure, she snaps back to reality just before penetration, orally pleasuring him instead to defuse the situation. Despite knowing it's wrong, she continues responding to his persistent advances, eventually giving in to his seduction—leading to an intense, forbidden affair filled with anal sex, humiliation, and erotic training.