Shinnosuke and his family go to the 20th century museum, a recreation of the 1970s World Expo in Osaka. His parents are exposed to nostalgia of their younger days, and are treated to the prospect of realizing their childhood fantasies once more. Unfortunately the curators of the museum have other plans of putting the future to an end, and living in the past century forever in their project Yesterday Once More. This plan causes all the adults to lose their memories of adulthood, and live in the 20th century forever! But what will happen to all the children if their parents refuse to grow up? Source: themanime.org/viewreview.php?id=952