While Doraemon is asleep, a famous thief comes and steals his cat-bell. Without his cat-bell, Doraemon starts to act more and more like a normal cat. In order to stop this, Nobita, Shizuka, ...

Nobita and Doraemon find a giant robot in pieces which they later assemble. It turns out to be a destructive weapon and the gang must save Earth from an imminent invasion.