Synopsis: Noby builds a gigantic robot from random parts he found at the North Pole. Thinking of the robot as a cool toy, he is having fun with it in the mirror world with Doraemon and Shizuka when they realize that the robot is actually not a toy, but a deadly weapon that can destroy buildings with a single blow. The three promise to keep this a secret, but Noby lets it slip when he meets Lyril, a mysterious girl who is looking for a robot. Noby then discovers the terrifying truth: Lyril has taken over the mirror world, building a secret base with plans to invade Earth! The Mecha Army could arrive at any moment to destroy cities and enslave humans. Can Noby and his gang stop them? A story of love, courage and friendship, the seventh tale of the Doraemon's Long Tales series!