Rinko, a wife who has been married for three years after a workplace romance, lives with her husband's younger sister, Yu, who moved to Tokyo to become a photographer. Yuu was a little younger than her girlfriend, Rinko, and loved her as if she were her real sister. One day, her husband was away from home on a business trip for three days. The two sisters-in-law are alone under one roof. Normally women should be able to live together without worrying about each other, but who is Yu?