Momotaro Morikawa, a car mechanic and single father, raises his daughter Kokone in near-future Japan as the 2020 Tokyo Olympics approach. His wife, Ikumi Shijima, died in an accident when Kokone was young, compelling Momotaro to conceal much of their family history while raising their daughter alone. Ikumi was the daughter of Isshin Shijima, chairman of the major automotive company Shijima Motors, and had pioneered innovative self-driving car technology. After eloping with Momotaro against her family's wishes and being disowned, the couple continued developing her research independently. Following Ikumi's death, Momotaro dedicated himself to completing her unfinished autonomous vehicle systems using a cracked tablet containing her research data and code.

Within Kokone's dream world of Heartland, Momotaro manifests as Peach, a skilled motorcycle rider and mechanic who designs vehicles in the kingdom's car-centric society. Peach serves loyally under the King (representing Isshin Shijima) but faces punishment for favoring motorcycles over car manufacturing. He allies with Princess Ancien (representing the younger Ikumi/Kokone) to combat the Colossus threat using her magic tablet, echoing his real-world collaboration with Ikumi. Peach's protective actions towards Ancien, including physically shielding her from danger, mirror Momotaro's role as a father and his past with Ikumi.

Momotaro's possession of Ikumi's research tablet becomes pivotal when Shijima Motors agents arrest him for alleged corporate espionage, accusing him of stealing the self-driving technology. This occurs three days before the Olympics opening ceremony, as Shijima Motors—now seeking to showcase the once-rejected technology—attempts to reclaim it through executive Watanabe (who appears as the antagonistic adviser Bewan in Heartland). From jail, Momotaro texts Kokone a warning not to trust Watanabe, including a photo of himself, Ikumi, and Watanabe from their past association at Shijima Motors, underscoring Watanabe's longstanding resentment over Momotaro's relationship with Ikumi and the technological legacy.

During the climax, Momotaro escapes custody and reunites with Kokone at Shijima Motors headquarters. Confronted by Watanabe on a high rafter, he physically reenacts Peach's protective gesture from Kokone's dreams by gripping her tightly to prevent a fall. Their survival of the plunge—cushioned by an inflatable balloon deployed by self-driving vehicles using Ikumi's technology—symbolically resolves the family's trauma. This event reveals to Kokone that her name blends Shijima Motors' motto "heart" (kokoro) and "wing" (hane), reconciling her parents' legacy with her identity. Post-climax credits scenes depict Momotaro's courtship with Ikumi and early tests of her software, affirming his enduring commitment to her vision.

A short spin-off film, *Ancien and the Magic Tablet: Another Princess*, explores Heartland's world without adding backstory or development for Momotaro/Peach beyond the original narrative.