The story began four years ago. High school student Kimidzuka Kimihiko was flying on an airplane and, as a result of an incident, met a girl detective who called herself “Siesta.” Then he became her assistant, working for the detective until she “died.” And now, our hero (Kimidzuka), recovering from the loss of his dear companion, tries to live an ordinary high school student’s life—but as we know, the past always hunts you, and our hero is no exception.