Renji Aso meets Chihiro Shindo at an abandoned train station one day after school, and returns to the same stations several days in a row to meet with her again, finally becoming friends with her on the third day. While out during Christmas heading to his friend's Christmas party, Hiro Hirono stops near a church where his bike his stolen by a girl who passes by chasing a purse snatcher. After catching up to her, he spends the rest of the night with her and finds out her name is Miyako Miyamura.

While ditching classes, Hiro runs into Miyako again, finding out that she is in the same year as him attending the same school, though in a different class. She finds out that he is already an established manga author which is the reason why he does not attend classes much. Kyosuke Tsutsumi continues to ponder over the brief shot he got of Kei running through the city on Christmas, though he does not recognize her. Renji meets again with Chihiro and becomes closer with her. He eventually finds out from her that she has a memory defect where she cannot remember anything past thirteen hours previous.

Renji continues to meets with Chihiro every day after school, though he wonders if he should continue with such a half-hearted attitude. It rains one day after school, so Renji does not go to meet Chihiro, thinking that she would not come under the circumstances, but she comes anyway and manages to catch a cold, something Renji feels terrible about later on. Hiro goes out during school with Miya into town and they have lunch at a café. After Hiro accidentally forgets her given name, Miyako leaves him behind at the café. Kyosuke quits the film club, and even breaks up with his girlfriend.

Renji sees Chihiro for the first time after she gets over her cold and apologizes for not coming last time. Renji asks her if she would like to write a novel with him, as she had said earlier that it was her dream to write one, but Chihiro gets very defensive and angry at his request. After talking with her more on the issue, Chihiro finally gives in to his persistence. Kyosuke sees Kei again in town and finally realizes she was the one he filmed on Christmas. Hiro meets with Miyako in town and she goes back to his place while he works on his manga. Miyako reads some of Hiro's manga, and as an act to show her gratitude, she cooks food for him. Kei walks in on them together, and runs off.

Renji brings Chihiro to his home where she meets his mother and Shuichi Kuze, though she has merely forgotten Shuichi many times over. After they eat, Chihiro gives Renji a notebook with her notes for her novel which he reads after she leaves for the day. He finds that the novel is rather depressing and representative of Chihiro's life. At school, Kei tries to get Miyako to leave Hiro alone so he will not have to repeat a year of school, but Miyako talks down to her the entire time. Kyosuke films Kei in the morning while she is taking a basketball shot, and she punches him in the gut for filming her without permission. He later asks her to go out with him via Hiro's help.

It turns out that Kyosuke asking Kei out was a ploy on his part as a lead in to ask her if she wanted to star in an amateur film he is making for an upcoming film festival. Hirono and Kyosuke get into an argument over the differences between being a professional and an amateur, ending with Kei interjecting, saying she has not decided if she will choose to be cast in Kyosuke's film or not. Later, Kei informs Miyako in an intense discussion that Miyako will eventually disappear from Hirono's heart (she actually says "I will erase you from his memories"). On Sunday, Kei gets hurt at the basketball match and Hirono stands up Miyako on a date they were supposed to go on to make sure Kei is all right. Meanwhile, Chihiro continues to write her novel and Renji helps her by borrowing a uniform from Shuichi so that they can enter the school's library to research materials for the novel.

Renji and Chihiro continue work on the novel at his school's library and they manage to get to around 70% complete. Afterwards, the two take a walk on the beach and Chihiro suddenly asks Renji if he wants to kiss her. This seemingly simple act throws Renji off balance and says that their relationship is not like that, which causes her to run away in tears. Renji breaks down, hoping she will not write down what just happened in her diary. The story shifts to a flashback of when Miyako was waiting for Hirono to show up for their date in the previous episode. Miyako continues to send him voice messages on his cell phone, first being angry for him not showing up, but later becoming increasingly deperate with each call as she does not want Hirono to ignore her. The story shifts back to the present in Hirono's room, with Hirono and Kei together. After Hirono leaves his room to get food, Kei discovers Miyako's messages before Hirono learns of thier existence, and promptly deletes them, as she vowed to "erase her from his memories".

Frustrated that none of her calls made it through to Hiro, Miyako therw her cell phone into a nearby fountain the night he stood her up. Hiro tries to call her repeatedly, but cannot get through due to this. Miyako later calls him and is reassured that Kei lied to her when she said Miyako had already disappeared from Hiro's heart. Chihiro and Renji continue work on the novel, and Chihiro is pushing herself with stress and lack of sleep so as to prolong her memories. She eventually collapses and is unconscious for over thirteen hours. When she finally awakes, Renji witnesses Chihiro's frantic state of not understanding why she has grown older or what happened to her left eye.

Hiro finds Miyako at a telephone booth in town and after a stroll on the beach where they kiss, Hiro takes her back to his place where they get intimate. The following morning, Kei finds Miyako in Hiro's bed, which causes her to run away in tears, eventually collapsing on the road as Kyosuke rushes up to her with his bike. Renji continues to stay with Chihiro despite the pain he feels and manages to smile when around her. Chihiro re-reads her diary three times and eventually comes to act like the person described in her diary, but she thinks that person is already dead. After hearing this, Renji vents his frustration and continuously repeats that this is not true.

Kyosuke confronts Hiro about what happened with Kei and tells him that he always does things half-way. Miyako calls Hiro to tell him that it is too painful to be with him since she does not want to be eventually forgotten by him. Hiro goes to see Kei and is able to come to an understanding with her, even though he is in love with Miyako. Right before she is going to leave town, Miyako calls Hiro one last time. The calls cuts out at a pivotal moment leading to Hiro rushing out on his bike and managing to find her at a public telephone near a church where they kiss.

Chihiro finishes her novel and wants Renji to read it, though does not want to be around when he does. Renji proposes they go out on a date, which Chihiro happily agrees to, though she promises Renji that they will become lovers for only one day. After their date, Renji confesses his love to her once again on the school balcony, and shortly after they have sex. Later that night, Chihiro gives Renji the novel to read, and she goes up to the school balcony to wait for him to finish. After realizing the bleak ending of the novel, Renji runs up to the balcony to meet Chihiro, though she tells him that they should break up while she can still say "I love you" and fully mean it. Chihiro throws all her diary pages containing accounts of Renji into the air, effectively forcing Renji to break up with her.

Renji searched for the pages of Chihiro's diary about him. He finds Chihiro at the station where they first met. Renji promises that he will find all the remaining pages of the remaining diary in which Chihirio tells him that '13 hours is a long time'. Chihiro still doesn't forget about Renji because for the past 13 hours the only thing that she though of was only the memories she had with renji. The three love stories of Renji x Chihiro, Hiro x Miyako, and Kyosuke x Kei ended a happy one. Yuko finally reunited with Yu at the old church. It ended happily ever after.