A nostalgia theme park called the 20th Century Expo is sweeping Japan, drawing adults back to relive the look and feel of the 1970s, and the organization behind it, Yesterday Once More, has bigger plans than simple nostalgia. When the grown-ups of Kasukabe start abandoning their responsibilities for the Expo's pull, five-year-old Shinnosuke finds his own parents among them and sets out to bring his family back before the past swallows their present for good.