Milk and Water

Sachiko and her dad have lived contentedly together for 7 years. One day, her dad decides to tell her the secret about their true connection, that he was not the man who had relationship with Sachiko's mother - who, all of a sudden, came back knocking his door after 6 months from the time they almost got to have sex, and dropped Sachiko to him. Having been told to take this story seriously, how will Sachiko understand this reality? How exactly does her dad feel about it? Will it ever effect the love and home they've built together for the past seven years?