Yuki Nakagawa is a 28-year-old single woman who works as a translator from home. It has been four years since she began living with her younger sister, Noriko, a university student. Yuki tends to have casual relationships with men. Noriko, on the other hand, has been dating her classmate Kazuya for three years. A dispute over her job prospects leads to an argument between the two. A few days later, Kazuya comes to visit Noriko. Unfortunately, Noriko is out, but Yuki offers Kazuya a drink to cheer him up. Before long, the two end up in each other’s arms—