Theme parks like 20th Century Expo, which reenacted the good old days of the 1970s (the latter years of Japan's rapid economic boom), had adults all across Japan spellbound. One day the parents left their kids behind and ventured off into the amusement parks. That was a scheme by "Yesterday Once More," a group that despises the 21st century and works to return Japan to the 20th century by instilling hopes and dreams in it. In order to coexist as a family in the twenty-first century, Shinnosuke and his parents, Hiroshi and Misae, struggle against the storyline of "Yesterday Once More."