Hikaru's husband's younger sister and her fiancé, Shigeki, begin staying at Hikaru's home for a while. Feeling lonely due to her husband's constant busyness, Hikaru finds herself increasingly drawn to Shigeki, who is kind and thoughtful. Though she knows it's wrong, she becomes emotionally stirred by his warmth and begins to experience the thrill of forbidden pleasure. The story captures Hikaru's inner turmoil and emotional conflict.