The story starts on the first day of a new school term (ie, April in Japan). Asai Chiaki, a very shy girl in the 2nd year junior high, meets Futami Yuuya, a transfer student who has joined her class on that day. He thinks Chiaki has her hair permed (which is banned in many Japanese schools) but her hair is naturally curly. She is annoyed with his over-friendliness but envies the way he is quickly accepted by the class.
One evening in the early summer, Chiaki receives two letters from a cram school, one addressed to herself and the other to Yuuya. She finds out he lives in Flat 204 of Second Green Heights while her home is Flat 204 of First Green Heights. She finds it uneasy to find his room is identical to hers. No, she doesn't like Yuuya! But her classmates thinks he is cheerful and kind.
One day Yuuya points out the girls in the class call each other by their nicknames except Chiaki, who is always called Asai-san. Her friends says that they have called her so ever since she moved there in the 3rd year of elementary school. Yuuya thinks the fact Chiaki was also a transfer student amusing and tells his history of changing schools. Then he proposes to give Chiaki a nickname but Chiaki angrily refuses it. Yuuya's reply is "You're always angry, Asai."
Later that day, Chiaki finds a first-year girl looking for something. She wonders if she should offer to help when the girl asks Chiaki if she has seen the key for the music room. Chiaki replies that she hasn't in a cold manner and then remembers Mr Shimomura, the music teacher, is not a particularly nice man. Suddenly Yuuya comes running towards the girl, shouting "I've found it!" Yes, he was helping this girl although he was on his way to the basketball club, which is known to be very strict about practice time.
That evening, while Chiaki is looking at Yuuya's room to see it twinkling, her mother tells her that they have received another letter to Yuuya and asks her to deliver it. It is a letter from his old place with the beautiful handwriting of a woman. Somehow Chiaki fails to deliver it then and does it on the next day.
At the entrance of Yuuya's house, she bumps into his mother. Summoned by her, Yuuya comes out of his room, the same room as Chiaki's. Chiaki is relieved by his shout, "Oh, it's from Tazawa-sensei (teacher)." Now Yuuya finds out that she lives in an identical flat. Later that night, she wonders how he behaved in his previous school, what kind of reply he is going to write and what he is doing now in his twinkling room.
On the next morning, Chiaki is met by boys in the class who tease her and Yuuya, saying "living in the same room." She shouts back, "He came here without my permission. I am not living at a similar address as him for a fun!" Surprisingly Yuuya retorts, "Same here!" Chiaki cannot hold tears back.
In the evening, she looks at his room over the road again but it is in darkness and without its twinkle. She regrets what she has been doing to him and wishes he would forgive her. Then Yuuya comes over to apologize. She does not think he has anything to apologize for. He admits he was excited by the idea of not only him and her but many more people living in a similar flat. There are so many people in the world and only very tiny part of them live in this place. He went on to wonder what she was doing, what she was thinking and how her room was arranged. As this made him feel a bit guilty, he shouted at her in the classroom.
Now it's Chiaki's turn to own up. She admitted she did the same thing. Yuuya joyously replies, "Oh, I'm glad. I was worried you may hate me." At his smile, Chiaki realises the reason why his room twinkles and why she cannot stop crying when she thinks of him. She confess to bewildered Yuuya, "I love you, Futami."
Three years later, Chiaki, organizing a class reunion, meets her old friends, who tell her she has changed. They think it is because of the other organizer, who just appears on the scene. Yuuya, Chiaki thinks, often looks at her as if he is looking at something twinkling.
Five years ago, there was a small rubber boat floating in Tokyo Bay. Two children, Ogata Noriaki and Ochiai Akane, were rescued from it.
Now the couple have grown up to become members of a fine-art club of a highschool, busy preparing for forthcoming art festival. Akane is the sub-leader of the club and is regarded by many of the junior girls as a major obstacle for them in their attempts to catch the heart of Noriaki who has become very popular. After Akane and Noriaki have gone home together, a friend tells the junior girls that the two have been going out for five years and their link is very strong due to a certain event that happened their elementary school days. At the corner of the art room, Matsue Miyuki smiles knowingly.
At the railway station, after jan-ken, Noriaki gets on the first train while Akane waits for the next one. Matsue comes and sits down next to Akane, asking why they take different trains every day when they get off at the same station. She quotes rumors saying they never phone each other or go out anywhere together. She asks if they are really going out or not but leaves without waiting for the answer.
On the next morning, Matsue walks with Akane to school. Asked why, she replies "Harassing you so that you and Noriaki will split." Matsue tells her that she loves him, too. "Then do something with your character" was Akane's reply.
Matsue keep harassing Akane and eventually Noriaki find it out. He worries about her as she looks depressed. Akane says she can cope with Matsue and she looked unwell because she was a little tired and hungry.
Akane is grateful that he worried for her but wishes he realize the true reason of her trouble. Then she catches Izumi, the nominal leader of the club, and orders him to make the list of members who are going to the club's sketch excursion after the art festival. Seeing this, her friends realize she is tougher than she looks.
At the club, she stains her skirt with paint and goes to the preparation room for benzine, where Matsue was waiting. She admits that her tactics have so far failed but complains Akane and Noriaki are not acting like a real couple. Asked what attracts her to Noriaki, Matsue lists his good points; tall, good-looking, bright, reserved, kind etc. Akane says that is not what Noriaki really is but what he pretends to be for her sake.
Akane explains what happened five years ago. Noriaki wanted to go to America and planned to sneak aboard a tanker in Tokyo Bay. His uncle worked on the ship and it was bound for US. She joined the plan and they used the rubber boat to reach the tanker. After a complete failure, their parents told them never to play with him/her again. Akane's parents even banned her going out after 7pm or traveling with her friends. But Noriaki told Akane that she was the only partner for his life and they should be patient until they grow up into an impeccable man and woman. Then he would marry her!
Matsue is not impressed that much but Akane says it was a real "adventure" for them and its consequence (the big search involving parents, relatives, teachers and police) made them realize what a big responsibility one must carry to go for an adventure.
In the meantime, Noriaki wonders what is troubling Akane. Then he finds out that her name is on the list of the sketch excursion.
Back in the art room, Matsue declares she will stop harassing her as there is no need for it. She can do whatever she wants while Akane and Noriaki passively wait for the circumstances to change. Then Noriaki comes to ask if she has got her parents permission over the excursion. "Not yet." Noriaki tries to persuade her to give up. Akane is not moved. She says, "We have repented enough and now it is a time to be what we really are again." Noriaki isn't happy. He reminds her that they decided to wait because of the difficulty and responsibility of going their own way. He shouts, "Do you think of the even of five years ago as something silly? I didn't expect you to have changed like this!" Something snapped in Akane. She fiercely shouts back "Who the hell do you think I am? You've forgotten even that, right? Don't think too little of me!"
On his way home, Noriaki ponders over her words. She should know all his efforts so far have been for her sake. Perhaps, five years is too long? At home, his mother tells him that Akane is at odds with her parents over her friendship with him and on hunger strike. Her mother was very sarcastic when she told it to his mother.
He recollects about the night of adventure. It was only her who joined the plan although he had told it to many others. Her excited attitude assured him, when he had not been too confident over his own plan. Yes, it is him who has forgotten. For whom has he been a good boy? What makes that girl distinct from the others? No! She is not a girl who waits, sleeping passively, for a prince!
On the next day, Noriaki did not turn up to the club. She wonders if she has lost his heart. But she cannot regret her action as she did not want him to change for her.
She walks to the railway station, followed by Matsue, who is now after her. But Noriaki was waiting for her with a bunch of flowers. "I'll walk you home."
One morning of the spring holiday, Kaoru opens the door of the wash room of the women's dorm of her college, hoping her night mare would end. But she finds three girls, not two.
The previous night, the "three" girls did a horror story-telling, where each of them carries a candle and extinguishes it when she has finished her story. After all the candles are gone, they count in turn and a ghost will add one more. "One", "Two", "Three", "Four" !?!?
When they put the light on again, they found there were four girls in the room. Yumi, Ryouko, Nori and Kaoru. It was obvious one girl appeared just now but strangely, no one can tell which. They ended their party, hoping the ghost would disappear with the morning light. Kaoru thought very hard about which was the invader. But the more she thought, the less solid her memory became.
Now the four have breakfast together. Suddenly Ryouko remember that a girl committed suicide in the dorm a few years ago. And she must be the extra one. Nori thinks the ghost may stay permanently. She suspect the dead girl now regrets her suicide and, as she can control others' memory, it would not be too difficult for her to stay around. Ryouko proposes to stay away from each other because it is not nice to look at each other with suspicion. Then Yumi remembers that Nori and she stayed in the dorm over the holiday because of their holiday job. Ryouko stayed because her home is being rebuilt. How about Kaoru? She cannot remember as the ghost has fiddled with her memory. But she now remembers that her boyfriend is in the men's dorm.
She runs to the men's dorm to fetch Shimada to solve the problem. But even he could not tell. Ryouko asks Shimada if he is sure that Kaoru is his girlfriend. After a moment of silence, he replies, "Of course!" Kaoru thanks him as she was worried.
The four girls live independently although at the beginning of the holiday they were going to spend their last spring holiday together.
Nori says the fact we realized there was an extra person although they could not tell who it was will be inconvenient for the ghost if she wants to stay. Nori warns the others that the ghost may try "replace" one of them with herself.
Kaoru is exhausted because of lack of sleep but finds comfort in the relationship with Shimada. He is the only thing she can trust now.
Her exhaustion has reached a critical level and one day she falls from the stairs. She has not fainted but fell asleep. In Kaoru's room, the three girls discuss what to do. Suddenly Yumi says she is thinking of going home. There is no point staying here with such fear and anxiety. Kaoru wakes up and says, "no!" They stayed to have a nice time together and whoever the ghost is, she is fond of all three of the girls. Nori agrees and Ryouko proposes to go back to square 1. Have a party to celebrate we have another friend!
After a really enjoyable party, Kaoru walks back to her room with Yumi. In front of her room, Yumi grabs Kaoru's wrist. She says, "I'm sorry but it was a fun. Good-bye." In her room, Yumi regrets that she did not trust anyone. If she had even one person she could trust, then things might have been different. Yes, she is the girl who committed suicide.
Kaoru is drunk and happy. They should have done this in the first place. "We can have fun. Me, Nori, Ryouko. Three of us... !!" She realizes she cannot remember anything about the fourth girl any more. She runs to Nori and Ryouko but they cannot remember, either.
On the next day, the girls tell it to Shimada, who turns out to be no better. He confesses that he was not sure if Kaoru was his girlfriend when he was asked. But he could not betray her trust.
The holiday is over and other students have come back. The dorm is less of a lonely place now. Kaoru asks, "Is this a more comfortable place for you now, Miss Stranger?"