When a new threat regresses the minds of the adults of Kasukabe back into children, its up to Shinnosuke and his friends to reclaim their parents from becoming trapped in the nostalgia of the 20th Century.

As the 21st century approaches, a new 20th-century museum has opened in town, for the adults to relive their childhood. However, the owners of the museum seem to have other plans for it. The adults start to behave strangely, and one morning, they abandon their children for the 20th-century museum. Shinnosuke, along with his friends, must now rescue his parents and stop the world from returning to the 20th century before they get captured.—Anime News Network