The Summer of Stickleback.

Set in Kyoto, 1990. Mizuho Oshima is a high school girl who hates her alcoholic mom, adores her father, and has a crush on school swim team member Sho Sugimoto. Her father lives with another women, but Mizuho hopes to reunite her family. Her mother then takes up with an Amerian soldier named Charlie and they become an item. This crushes Mizuho's hopes of reuniting her family. Mizuho then seduces her mother's lover ...