Nobita stumbles onto proof that folklore is real, and the show treats this not as spectacle but as a homework assignment that accidentally rewrites history. The time camera stops being a gadget and becomes a window into whether the stories adults tell about heroes are true or invented. It's the kind of premise that only works when you're nine years old and still believe the line between legend and fact is thin enough to photograph.
Nobita needs to complete a summer homework assignment researching his town's history, so he and Doraemon break out a time camera to photograph local landmarks across different eras. One mysterious shot shows a figure that looks suspiciously like Momotaro, the legendary peach boy from Japanese folklore, hauling treasure through the streets. The mystery deepens when a foreign visitor arrives with an old portrait that appears to be an actual photograph of the same man in samurai clothing. Intrigued by the possibility that a folk tale might actually be rooted in real events, Nobita becomes determined to trace the truth. He and Doraemon decide to journey backward through time itself to investigate whether Momotaro was genuinely a historical figure, and if so, what his real story actually was. What begins as simple homework spirals into a historical detective adventure that challenges everything they thought they knew about one of Japan's most famous legends.