A lonesome college student, Jiro, is spending his 20th birthday alone, when suddenly, a beautiful girl turns up. The few hours that he spends with her are the most incredible moments of his life and Jiro is overwhelmed by his good-fortune in meeting her. But his happiness does not last long as she disappears as suddenly as she appeared. A year later, on his 21st birthday, Jiro runs into her again at the same restaurant, where she saves him and countless others from a crazy assassin. She looks the same, but this time she is somehow different. It is the beginning of a relationship that would change his life forever.