Yui enjoyed a happy married life until her husband’s job transfer led them to relocate near his hometown. While searching for a new home, they decided to temporarily stay at his parents’ house. However, the household included his younger brother, who was a ronin preparing for university entrance exams. The family atmosphere quickly made Yui feel intense pressure. The younger brother admired Yui’s intelligence and academic abilities, pleading with her to tutor him. Out of kindness, Yui agreed and began helping him study. But as time passed, he developed a strong physical attraction toward her, gradually shifting his feelings into forbidden territory. Shocked and uneasy, Yui found herself emotionally overwhelmed and helplessly drawn into an increasingly complicated and taboo relationship.