Tale of a Raindrop(雨粒の小さな歴史)

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.