Shinnosuke Nohara, a five-year-old kindergarten student commonly called Shin-chan, anchors the film's events. His character blends crude humor, perceptiveness, and unexpected maturity amid Kasukabe's crisis. Shin-chan initiates the story with typical inappropriate antics—mooning and directing off-color jokes at his teacher Miss Yoshinaga—yet displays sharp awareness upon noticing behavioral shifts in others, especially Miss Yoshinaga's uncharacteristic lack of reaction.

During a shopping mall visit, Shin-chan encounters clone impostors of family members. A clone attempts to lure him away before the mysterious woman Jackie intervenes, forging his connection to the conflict. As Kasukabe falls to konjaclone duplicates created by antagonist Amigo Suzuki, Shin-chan flees the city with his family and Jackie. Captured at Amigo Suzuki's base, he witnesses the mass production of konjaclone impostors through biotechnology.

At the climax, Shin-chan proves pivotal in the samba duel between Jackie and Amigo Suzuki. Spotting Jackie's hesitation, he urges her to "dance as she likes," demonstrating unrestrained moves including mooning. This support inspires Jackie to incorporate his unconventional style, shifting public favor and defeating Amigo Suzuki. Shin-chan's spontaneous problem-solving and influence disrupt the antagonist's plan for global conformity via psychedelic samba.

Post-resolution, Jackie gifts Shin-chan her samba whistle in gratitude. Throughout, he balances characteristic irreverence with perceptiveness and decisive action—evident in his dance duel support and clone impostor interactions.