Doraemon: Nobita to Tetsujin Heidan (1986)

After finding a strange metal block in the North Pole, Nobita takes the enormous object to his house together with a strange sphere. To his surprise, metal blocks start falling from the sky and keep landing on his backyard. They are components of a giant robot that Doraemon and Nobita secretly assemble at a mirror world created by one of Doraemon’s gadgets. The huge automaton belongs to a mysterious girl named Riruru. She has come here because a platoon of iron men is heading towards Earth to enslave the entire human population. Doraemon and his friends must then defeat the mechanized menace to save mankind.

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