In the midst of their troublesome teenage antics, three high school delinquents—Kenji, Ota, and Asakura—spend their free time indulging in lighthearted bullying, leaving a wake of uncertainty behind them. Their lives are a constant juxtaposition of chaos and indifference. When Ota jokingly suggests that they pay a visit to the rival gang over at Marutake High to settle old scores, Kenji, caught up in the moment, agrees. However, their excitement quickly fades as they realize they have no idea where Marutake actually is.
As the story unfolds, we find Kenji wandering the streets, lost in thought, when he unexpectedly witnesses a bold robbery. In a twist of fate, a passing musician hands him a guitar, using it to thwart the thief, and from that moment, the instrument becomes Kenji's prize catch. Eager to share this newfound treasure, he brings it to his friends the next day. Thus begins their clumsy journey into the world of music, yet their lack of musical talent results in sounds that resemble discord rather than melody. They resort to stealing instruments from school, unwittingly discovering that Kenji's newly acquired bass is the spark that ignites their audiovisual chaos.
The trio's first and only audience member is Aya, who inquires about the name of their burgeoning band. Asakura comes up with the moniker "Kobujutsu"—a nod to ancient martial arts— which Kenji adopts without a second thought. Their venture into music is fraught with missteps and surprises, as they gradually stumble upon a sound that oscillates between unpleasant and irresistible.
Interwoven throughout the film are glimpses of the Mohawk-sporting gang of Marutake, led by Ôba, who mistakenly believes Kenji is orchestrating conflicts against his members. This misunderstanding sets off a series of escalating events, prompting Ôba to devise a plan to teach Kenji a lesson he won’t soon forget. As time progresses, Asakura uncovers a striking musical relationship between their band and Kobijitsu, a charming acoustic folk trio headed by Morita. Instead of confronting them directly, Kenji opts to experience their sound, leading to an enthralling encounter that grows mutual interest. In turn, Morita is captivated by the raw energy of Kenji's band and invites them to perform together at an upcoming rock festival.
Eager but ultimately disillusioned, Kenji initially embraces the opportunity, but as practices unfold, boredom sets in. Despite Aya's attempts to reignite his passion for music, she is unable to sway his indifference, leading to a brief altercation that sends her away, leaving Kenji alone and defeated.
On the festival day, drama ensues as Kenji finds himself confronted by Ôba's gang. As tensions rise, Kenji shatters his bass and, in a moment of spontaneity, pulls out a recorder and begins to play, leaving Om and his gang in a stunned silence as they pursue him. Meanwhile, Kobujutsu had planned to perform separately as Kobijitsu, but Morita's band takes the stage first. Just as their set is about to reach a crescendo, Morita's guitar snaps, and they leave the stage in dismay. Seeing that Kenji is nowhere to be found heightens the anxiety for Ota and Asakura, who stand frozen on stage.
In a dramatic turn of events, Kenji bursts onto the stage, still under chase from Ôba's gang, playing his recorder with fervor. Rejoining Kobujutsu, they combine their efforts, with Morita’s group joining in on the performance. The crowd becomes captivated, and as they finish, Kenji's face lights up with the spark of renewed passion as he sings to the audience.
However, the following day, the mood shifts as Kenji reverts to his usual stoic self. In an empty classroom, Aya has a heartfelt conversation with him, where he reveals the band’s dissolution. Heartbroken, she is then taken by surprise when Kenji casually asks her if she would like to go to Disneyland with him. Observing this interaction, Ota leaves swiftly, turning to Asakura with thoughts of reuniting the band, convinced that Kenji would likely be on board by the end of the day.
