Aikagi means "spare key" in Japanese, and this film presents a story of love and remembrance. Even if the owner of the key has left, the memories remain. Yukari (Hirosue Ryoko) and Hiroaki (Tamayama Tetsuji) have been together for eight years. Though they are both constantly busy with work and do not see each other often, Yukari believes that they will always be together. Just before Christmas, the couple finally has a chance to meet up, but Hiroaki tells her that he has found someone else and breaks up with her. The next day, a heartbroken Yukari cuts short her hair. When she sees Hiroaki's spare key, all the past memories come rushing back. Yukari decides to give him one last present.