On Christmas Eve, Hiro Hirono has his bicycle stolen by a girl who is chasing a thief that snatched her purse. He pursues them, only to find the girl passed out and his bike wrecked. The girl, Miyako Miyamura, soon regains consciousness, and they start talking. Once he confirms she is all right, they wind up spending Christmas Eve together. Later, Hiro discovers that Miyako goes to the same school he does, and they begin to spend more and more time together, with Miyako developing feelings for Hiro. Kei Shindou—Hiro's childhood friend who has harbored a crush on him for a long time—starts to feel jealous, leading to a love triangle.
The series also follows the story of Renji Asou. One day, he encounters Chihiro Shindou, Kei Shindou's twin sister, at an abandoned train station. Although she is very timid, they get along quite well and begin meeting at the same spot every day. However, Renji learns that Chihiro was in a car accident years ago and, as a result, suffers from a condition where her memory only lasts for 13 hours. Despite this, after discovering that Chihiro's dream is to write a novel, Renji resolves to help her achieve that dream while also trying to help her overcome the challenges posed by her condition.