Nobita stumbles into a real war he never asked for, and Doraemon can't magic his way out of it this time. The jealousy that kicks everything off, wanting something better than Suneo's toy, becomes completely meaningless the moment a fallen robot forces them into defending the planet. What starts as a kid's wish for one-upmanship becomes a desperate fight where a gadget-loving cat and an ordinary boy are the only ones standing between Earth and annihilation.

Nobita wants a robot to rival Suneo's flashy new toy, but Doraemon refuses to build one for him. That changes when Nobita stumbles on pieces of a mysterious robot that fell from the sky. He and Doraemon collect the parts and assemble them into a giant robot named Zanda Claus. Zanda Claus is no plaything: the pair learn it is a powerful weapon in the struggle against a Robot Army that plans to attack Earth and enslave its people. With the invasion drawing near, a mysterious girl called Riruru appears, searching for the robot. The film sets this looming threat alongside the comedy the franchise is known for.