The moment all the adults vanish into a nostalgia trap, Shin-chan stops being a gag machine and becomes the only thing standing between his family and a world that decided growing up was a mistake. Comedy doesn't disappear, it sharpens, because every joke now has weight behind it. A five-year-old saving his parents from their own arrested development is absurd enough to make you laugh. It's also the only thing that could make you care whether he succeeds.
A new museum dedicated to 20th-century nostalgia opens in town, promising adults a chance to relive the glory days. But something sinister lurks behind the rose-tinted facade. One morning, every grown-up in the city vanishes into the museum, leaving their children bewildered and abandoned. Among them is Shinnosuke Nohara, a five-year-old with more courage than common sense, who realizes the adults have fallen under the museum's spell and won't be coming home. With his ragtag group of kindergarten friends, Shinnosuke launches a desperate rescue mission to pull his parents and the entire adult population back to reality. What starts as a comedic adventure quickly becomes a race against time, as the museum's operators reveal their true agenda: permanently trapping everyone in a sanitized version of the past. The kids must figure out how to free their parents before the entire world regresses into a beautiful, empty dream from which no one wants to wake. This film balances Shin-chan's signature irreverent humor with genuine stakes and surprisingly emotional moments about growing up and letting go.