Okazaki Shimako is an office worker for a fashion company who believes her boyfriend is going to propose to her on Christmas Eve, and is planning on quitting her job. Instead he dumps her by phone right before their date. As she’s home trying to understand what has happened her younger sister whom she hasn’t seen in 18 years shows up…

Minori couldn’t be more different from her older sister. Shimako is straight-laced while she is wild and a free spirit who sleeps around and lives life fairly full. But Minori needs a place to live, and moves into Shimako’s apartment. Just what effect will Minori’s appearance have on Shimako’s love life? Or is it the other way around