在一个浪漫的夏天，一切由美嘉遗失的手机开始。美嘉的同学，弘树拾到了手机并联络她，从而开始了两人亲密的关系。可是，弘树却在感情最好的时候不告而别。极度失望的美嘉从此拒绝谈恋爱。直至优的出现和对她关怀，最终使她再次打开心扉并展开了两人的恋情。然而，在平安夜当晚，美嘉发现了弘树离开的真正理由...

This is the story of a high school girl named Mika (Yui Aragaki) who falls in love with her schoolmate Hiro (Haruma Miura). A summer romance started when Mika lost and retrieving her cell phone and begins to recieve calls from Hiroko. While their love becomes more intimate, Hiro leaves her without telling the reason. Despairingly, Mika stop herself from being in love again. Later, she meets a guy named Yu (Keisuke Koide) who attempts to make her happy. Mika opens her heart again and strat dating Yu. However, on the night of Christmas Eve, Mika discover the real reason why Hiro is gone...