Noboru moves in with his older brother's household to prepare for his exams. He begins receiving tutoring from his beloved sister-in-law, Yuki, and finds himself captivated by her warmth and breath. One day, he accidentally discovers Yuki masturbating, and his emotions surge uncontrollably. At that moment, Yuki gently guides Noboru's hand to her breasts, rapidly deepening their relationship. The two grow closer each day, their bodies constantly touching as they passionately indulge in each other—until suddenly, the older brother returns home, setting the stage for an unexpected turn of events.