Separated from his father, Kaoru Nishimi transfers to a high school in Kyushu, where his uncle lives. However, on his first day at school, unable to cope with an unfamiliar environment and looks of curiosity from all around, Kaoru is overcome with nausea. He runs out of class and heads for the roof of the school in a panic, but waiting for him there is Sentaro Kawabuchi.

After Kaoru witnesses Sentaro playing the drums one day, the sounds of jazz keep echoing in his head. Shortly afterwards, a visitor comes to the record shop run by the father of Ritsuko, a classmate of Kaoru's. Sentaro chats with Junichi Katsuragi, whom he affectionately calls "Brother Jun", and then the two launch into an impromptu session in the basement studio. Kaoru can't conceal his excitement at seeing a live jazz session for the first time ever.

Over the summer at the beach, Kaoru and friends meet the beautiful Yurika Fukahori, who's a year older than them. Sentaro falls in love at first sight with the sophisticated girl. Noticing that Sentaro's efforts at their daily jazz practice are halfhearted, Kaoru arranges a double date with Yurika on Sentaro's behalf. The three of them and Ritsuko go on a picnic in a nearby mountain, but it doesn't go quite as planned...

One day near Christmas, Junichi returns from Tokyo, bringing with him an offer of a gig for the pleased Sentaro and Kaoru. The location is a jazz bar in the nearby downtown area and the two boys, who have never played for an audience before, are equally full of nervousness and anticipation. On the other hand, after Kaoru suddenly declared his love for Ritsuko days earlier, relations between the two have been strained...

Ever since the kissing incident, the relationship between Kaoru and Ritsuko has deteriorated. Feeling awkward about visiting the record shop, Kaoru enters the New Year without showing up once at jazz practice. But one day, he receives a letter that contains information about his mother’s present situation. And so, Kaoru heads for Tokyo to be reunited with the mother he hasn’t seen for over a decade, with Sentaro tagging along.

Kaoru and the rest have moved on to their second year of high school, and with the new school year comes a new classmate, Seiji Matsuoka, a flamboyant Beatles fan right down to the mushroom cut. But Seiji also fronts his own rock band and invites Sentaro to be the drummer. Sen refuses at first, but after hearing about Seiji's troubles, he feels sympathy for the pop music enthusiast. Finally, Sentaro agrees to join the band, but what about his passion for jazz…?

Sentaro is busy practicing with Seiji’s band, Olympus, while Kaoru has been chosen as the class representative for the school festival, and the distance between the two widens. On the day of the festival, as Kaoru’s eyes fall on Olympus and the appreciative crowd formed around it, he can’t hold back the flood of painful emotions. However, unexpected trouble occurs up on stage…

Kaoru's new-found popularity among female classmates after his performance with Sentaro causes Ritsuko to question her true feelings for him. Yurika comes upon Junichi and follows him back to his new apartment where she confronts him about a kiss they had shared at the record shop. Junichi unsuccessfully attempts to scare her away and her stubbornness, even going so far as to cut her hair to prove her point, forces Junichi to remember his regrets during his time as a member of the Japanese Communist Party in college. At school, Sentaro overhears students talking about Yurika's change in behavior and appearance and assumes that Junichi had done something to her. He goes to Junichi's apartment to confront him only to discover Yurika there with him. Sentaro tells Kaoru about what he had seen but Kaoru scolds him for not being aware that there was already someone in love with him. Sentaro soon realizes that the person Kaoru had been talking about was Ritsuko.

Junichi is offered a chance to work for a friend's publishing company in Tokyo and decides to leave the town to never return. Sentaro and Ritsuko attend the Christmas mass together while Kaoru decides to attend a Christmas party at Seiji's house, to distance himself from them. Finally aware of Ritsuko's feelings for him, Sentaro apologizes to her for never had realized before, but the two end up renewing their conviction that they are just like family to each other. Kaoru insists that Sentaro should fix his broken friendship with Junichi before he departs, even slapping him for it. Sentaro then challenges Junchi to one last jamming session with the band, to which he attends. The train taking Junichi to Tokyo is about to leave when he is approached by Yurika, begging to take her with him, but he insists that they should part ways. Just before the train starts moving, Junichi hears Yurika's parents at the station, angry at her for leaving a matchmaking meeting they arranged for her. Junichi pulls her into the train at the last moment, and the two embrace each other as the train leaves the city. Back at the record store, Kaoru opens the piano cover and finds the blue gloves Ritsuko knitted for him.

Sentaro’s love for Yurika has a sad ending as she eloped with Junichi. Meanwhile, Kaoru and Ritsuko have slowly been getting closer since the Christmas incident. Kaoru just can’t seem to take the next step, but when Ritsuko visits him while he’s recovering from a cold, Kaoru declares his feelings for her for the second time. And then, during the summer of their third year, Sentaro gets some unexpected news…

After learning of his stepfather’s homecoming, Sentaro intends to leave for good without telling anyone…except someone is waiting for him outside! Later, as the school festival draws near, Kaoru and Sen stress out over their competition with Seiji, until they add a new member to their group. Then, on the eve of the festival, an event occurs that will change their lives forever!

Graduation is at hand for Kaoru and Ritsuko, and there is still no word from Sentaro. While studying at Ritsuko's house, Kaoru tries to get more intimate with her, but she rejects him after he tells her he is happy that Sentaro is not there to get between them. Kaoru apologizes to her, but he reveals that he is leaving after graduation to go to college in Tokyo. After graduation, he stands outside the record shop and tells Ritsuko that he's happy he met her. On the day of his departure, he is seen off by his aunt, his cousin and Mukae. Just as the train starts leaving, he sees Ritsuko running along the train, and they manage to exchange one last glance before he leaves town for college. Eight years pass, and Kaoru is a resident doctor. One day, he meets Yurika and she shows him a picture of a friend's wedding on a small island, and he recognizes Sentaro in the photo. He rushes to the island, and learns that Sentaro is now a priest in training at the local church. Kaoru sees Sentaro's drums in the church, and starts to play Moanin' on the church organ. Sentaro hears, and goes to the church to join in on drums. The priest arrives and scolds Sentaro for playing the drums without permission, and Sentaro and Kaoru run out of the church and down the slope. Near the bottom of the slope, they reunite with Ritsuko, who is holding a postcard from Yurika about Sentaro's whereabouts.