Mikako Kouda is a 10th grader studying fashion design at the Yazawa Fine Arts School. All her life, she's lived next door to Tsutomu Yamaguchi. When they were in preschool, high school girls used to make a fuss over him because his name matched an old song, "Yamaguchi-san'chi no Tsutomu-kun" ("Tsutomu of the Yamaguchis' House"). Now, Tsutomu is popular again because he looks just like the popular singer Ken Nakagawa, and Mikako is annoyed by all the attention he's getting. Mikako complains about it to her friends Risa and Pii-chan.
Mikako comes home and finds Mariko Nakasu, nicknamed "Nice Body-ko," one of the most attractive girls at school, kissing Tsutomu goodbye. Tsutomu tries to explain, Mikako turns to leave, Tsutomu stops her, Mikako slaps him... they take their quarrel to the Blue Parrot, a nearby bar owned by Hiroaki "Toku-chan" Tokumori, their upstairs neighbor who has always been like a big brother to them. He gives them orange juice and calms them down. Mikako leaves while Tsutomu is in the bathroom washing the lipstick off his face. Tsutomu tells Toku-chan that having lived next door to Mikako all his life, he's starting to feel crowded by her.
Mikako feeds a stray kitten in the park. She curls up with it in the shelter of an elephant-shaped slide. In the sixth grade, when her parents told her they were getting divorced, she decided to run away from home and ended up in that same place. Tsutomu found her and took her home. She was crying, but not because she was sad, she was crying because she was happy he had come to save her.
When Mikako hasn't come home by nearly midnight, her friends and neighbors start to worry, especially since there have been reports of a molester in the neighborhood recently. Mikako, who has fallen asleep, wakes up and sees a shadowy figure looming over her. She screams, and Tsutomu rushes up and saves her. The "shadowy figure" turns out to just be Noriji, the superintendent of the apartment building, looking for Mikako, and Mikako and her mother convince him to let them keep the stray kitten. Mikako apologizes to Tsutomu, and they say goodnight to each other.
Mikako's mother Ruriko is the artist and writer of a successful girls' comic book called "Futari no Fantasia" ("Fantasia for Two"), but Mikako doesn't understand those kinds of romantic feelings at all.
Tsutomu promises Mikako he'll go shopping for toys and food and things for Kuro ("Black"), as she's named her kitten, after school. He used to look like a little monkey, but Mikako decides that if you don't know him, he's a pretty good-looking monkey. She wonders if it's only because he looks like a celebrity that he's so popular. A girl gives Tsutomu a love letter in the train station.
Tsutomu's friends Yuusuke and Jirou persuade him to cancel his appointment with Mikako and go out with Body-ko instead, because she's said she'll introduce them to some friends of hers. Mikako gets so angry at him, she can't go to class. Risa suggests that it's because she likes Tsutomu that she's so upset, but Mikako denies it. She goes back to class and sews with a vengeance.
That night, all the girls are making a fuss over Tsutomu, so Yuusuke tells him to take Body-ko and leave. In the street, Tsutomu sees Mikako and Risa and hides. Body-ko asks him if Mikako is really just a childhood friend to him. He says yes, and Body-ko asks him to go steady with her. He says he needs to think about it. He can't tell if she's dating him seriously or just teasing.
The next day, Tsutomu tries to apologize to Mikako, but she won't listen. She tells Risa it's because it can't be helped, Tsutomu has things that are more important to him than her, so even if he says he's sorry, he doesn't mean it. Risa says, "Even just a childhood friend can break your heart, can't they?"
Body-ko surprises Tsutomu cutting class, sitting alone on the steps. He agrees to go steady with her.
Mikako thinks, If this is heartbreak, I don't ever want to fall in love. I couldn't bear it.
Mikako learns that the day before, when she rushed off to school early to avoid meeting Tsutomu, he brought over a bag full of different kinds of cat food and cat toys. She goes over to his house to apologize. His mother tells her he's still asleep, but she can go on in and wake him up. Mikako swats Tsutomu on the head with a magazine, then notices it's pornographic. Repulsed yet intrigued, she leafs through it until he wakes up and snatches it away from her. She apologizes to him while he's shaving. He suggest they go together to buy more of the food Kuro likes, but then he gets a phone call from a distraught Body-ko, begging him to come over. Mikako urges him to ignore her, but he says he can't since they're going steady.
When Tsutomu reaches Body-ko's apartment, she has completely forgotten that she called him. She had just been trying to program her VCR and panicked and called him when it didn't work. He gets to see a totally different side of her, though, he sees a junior high school photograph of her looking cute, young, and innocent, and when he guesses that the boy with her is her first love, Body-ko blushes to her ears. Tsutomu tells her he likes her better without makeup. When he starts to leave, she is surprised that he didn't come over with any hidden intentions. Tsutomu and Mikako go out cat food shopping, but Mikako isn't satisfied and goes alone to the Blue Parrot. Toku-chan tells her it's only natural that kids her and Tsutomu's age want to date, but Mikako says she doesn't; when you fall in love, you just get your feelings swung around and you suffer. Toku-chan asks her if she's had her feelings swung around by someone.
Body-ko surprises everyone, Tsutomu included, by showing up at school with a new innocent, cute, natural look. The news flies all over school that Body-ko and Tsutomu are going steady. Mikako can't concentrate on her work and has to stay after school to finish. When she leaves, she finds Tsutomu and Yuusuke waiting; Risa asked Tsutomu to walk Mikako home since she'd be going home after dark. Mikako makes a fuss over Yuusuke's Super Cub scooter, then Body-ko comes out and takes hold of Tsutomu, and Mikako ends up getting a ride home with Yuusuke. Mikako invites Yuusuke in for a rice omelet and they reappraise each other. Tsutomu comes home as Yuusuke is leaving, and Yuusuke says, "Your childhood friend is cute. Mind if I try for her?
Mikako bleaches her hair blonde and revs up her personality.
Yuusuke invites Mikako on a date at an amusement park, saying he has free tickets. Jirou invites himself along, and Mikako invites Risa. Tsutomu doesn't want to, but just then Body-ko shows up and says they'll go too. However, on the planned day, both Risa and Jirou have to cancel. To avoid dealing with Body-ko, Mikako coyly goes off with Yuusuke, to Tsutomu's dismay.
Body-ko realizes that Tsutomu is jealous, and also realizes how serious she has become about him. While he's trying to comfort her, some young girls mistake him for Ken Nakagawa. A crowd gathers, and he and Body-ko are forced to flee. Mikako and Yuusuke overhear some people saying that Ken Nakagawa is at the park with a beautiful model and guess what has happened. Yuusuke is trying to wear Mikako out on the rides so he can put some moves on her, but she's proving indefatiguable.
Tsutomu and Body-ko find some peace and quiet on the ferris wheel and have a heart-to-heart talk. He couldn't help worrying about Mikako once Yuusuke took an interest in her, and worrying even more when Mikako responded. Body-ko says she understands, the boy in the photograph in her apartment was her own childhood friend. She felt caged in, though, and decided to broaden her horizons by leaving home and dating lots of different men. However, they all left her feeling empty. She thought Tsutomu might be different, but she's going home for spring vacation and will see him again. Tsutomu says that at first he thought Body-ko was beautiful, but... strange... but now he knows differently, but... "You like me, but second-best?" Body-ko completes his sentence for him.
They get off the ride and meet up with Yuusuke. He says he's given up on Mikako, who's still riding the roller coaster over and over. Tsutomu kicks him in the shin and goes off to find her. Mikako is starting to feel sick, but keeps riding, trying to shake off her unhappiness.
Meanwhile, Ruriko is drinking at the Blue Parrot. She reminds Toku-chan of the summer Mikako was in the third grade, when Mikako suddenly pierced her own ears. She confesses that it was her fault, Tsutomu had gone off to his grandparents' house in the country, and she jokingly told Mikako that Tsutomu might like it there and never come back. Whenever something happened to Mikako, she would do something to her appearance to cheer herself up. When her parents got a divorce, she pierced a third hole in her ear. Now, Ruriko worries about what happened to make Mikako dye her hair blonde.
Mikako gets off the roller coaster and gets a drink. She can overhear people talking about her. Tsutomu finds her and says, laughing, "With that hair, no matter where you are, I'll be able to find you." Body-ko and Yuusuke aren't where Tsutomu left them. Then Ken Nakagawa's fans spot them and they have to flee.
Mikako thinks that Tsutomu was dumped by Body-ko for Yuusuke and his Cub scooter and feels sorry for Tsutomu. He bursts out laughing and says Body-ko has a "favorite" she's holding out for. Yuusuke takes Body-ko home, but she won't let him into her apartment or go out with him. In a serious moment, he tells her to call him if she ever needs to talk again. (That day at the amusement park, she told him she wanted to stop playing around and love someone with all her heart.) Body-ko enters her apartment, hugs the photograph, and says, "I'm home, Shuu-chan."
It's the last day of the school year. School tradition has all the students wear their flashiest clothes on special occasions like the school closing ceremony, because Principal Yazawa likes flashy styles. That night, there's a students' party at a nightclub. While they're alone keeping a table while their friends are getting food, Mikako asks Tsutomu to explain why he and Body-ko split up. He says he had a "favorite," too. Mikako thinks Tsutomu is trying to put on a show of strength and feels sorry for him again.
Over spring vacation, Tsutomu goes away for ten days to a training camp to get a motorbike license. While he's gone, Ruriko exerts herself to cheer up a mopey Mikako. Mikako persuades her mother to buy her a Cub scooter so Tsutomu can drive her around. Yuusuke helps her pick one out, but afterwards leaves her in a hurry because he thinks he sees Body-ko. It turns out to be someone else, and he feels like a fool. Tsutomu comes home and Mikako shows him her new scooter "Sally," but by law, Tsutomu can't carry her as a passenger until he's had his license for one year. Mikako won't let him ride Sally by himself, so she impounds Sally for a year.