Yuu, a close friend of my mother, suddenly came to stay at our house. Usually cheerful and energetic, she seemed unusually lonely this time, as if hiding some personal troubles. When I tried to ask her about it, she clammed up, deepening the mystery. That night, I accidentally caught her masturbating. After that, every time I saw her, my perception of her changed completely. The feelings that had quietly begun to stir deep within my heart gradually began to grow stronger.