After saving a drowning stray dog he names Ichi, Nobita Nobi keeps taking in more strays until Doraemon suggests relocating them to a safe prehistoric era. A timing error strands the animals a thousand years earlier than planned, where they evolve into an advanced civilization of their own. When Nobita, Doraemon, Shizuka Minamoto, Suneo Honekawa, and Takeshi Gouda go looking for Ichi, they meet Nekojara, a corrupt official descended from cats who is plotting revenge on humans for abandoning animals, just as a swarm of asteroids closes in on that world.