This is a story of a young woman and her coming of age in Japan. In the winter before her college graduation, Michiru received a letter from a girl. Apparently, they are sisters who shared the same father. The letter explained their father who has left Michiru from her birth. Even though she had never cared about him, the fact about his existence spread within her. As she explored about him, she experiences irresistible youth and separations in her life. The youth of a girl is 'like the music pouring out from the world,' and fragile like a raindrop.