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. To their shock, the final shot shows Momotaro, the folk hero of Japanese legend, pulling a cart piled with treasure. The mystery deepens when Nobita's mother meets a foreigner who shows the kids a small, almost photographic picture, handed down from his ancestors, of a man in samurai dress who looks exactly like Momotaro. The visitor has come to Japan to learn where it came from. Starting to suspect that Momotaro may have really existed, Nobita sets off into Japan's past with Doraemon, Shizuka, Takeshi and Suneo to solve the mystery.