Two years after the disastrous launch of an experimental 7G cellular network that warped reality, Japan has been left devastated with civilization reduced to various scattered, isolated settlements. Strange phenomena are now commonplace throughout the country such as the people of the town of Agano being transformed into intelligent animals once they reach the age of 21. Shizuru Chikura, Nadeshiko Hoshi, Reimi Kuga, and Akira Shinonome are four students native to Agano who are left to wonder about their future, knowing they will inevitably turn into animals as well once they come of age. They then find a newspaper showing that their missing classmate Yoka Nakatomi is still alive in Ikebukuro, but have no way of getting there. That night, Shizuru finds a train conductor's cap and returns it to Tairo Zenjiro, who suddenly regains his sanity and reveals he has a grudge against Pontaro, the inventor of 7G, and seeks to get revenge on him. Unable to leave Agano himself, Zenjiro teaches Shizuru how to operate an abandoned train. Nadeshiko, Remi, Akira, and Yoka's dog Pochi decide to accompany Shizuru and they begin the long trek to Ikebukuro.