One day, the Nohara family met a mysterious alien from outer space named Shiriri. On being basked by a ray emitted by Shiriri, Hiroshi and Misae became 25 years younger and appeared as kids. To be able to return into adult form, they must find Shiriri's father, who is somewhere in Japan. This situation, which initially started with Shinnosuke's family and later his friends, gradually involves the entire of Japan.