The movie’s plot involves Nobita, who throws a temper tantrum because he wants a really large RC toy robot in order to upstage the rich kid, Suneo, who has been showing off the new robot that his cousin made. His fit makes Doraemon angry and he uses his Anywhere Door to get anyway from the summer heat cool off at the North Pole. Sometime later, Nobita follows and a discovers a strange bowling ball-like orb which starts blinking with a pulsating light, and summons what looks like a giant robot´s foot. After Nobita uses the foot to sled down, crashing into his room through the Anywhere Door, the bowling ball follows him home through the door and another robot piece falls into his backyard. A frozen Doraemon follows soon after, covered in ice before being thawed out and with a cold. Learning of the robot parts, Doraemon admits to Nobita that he has nothing to do with it as the two use the Opposite World Entrance Oil and the Roll-Up Fishing Hole to enter the World Inside the Mirror, an alternate mirror world without people. There, they built the robot which Nobita christens the name “Zanda Cross” as he believed the sphere summoning the parts is from Santa Clause.
Using a brain wave controller that Doraemon pulls out of his pocket, Nobita has the robot perform gymnastic maneuvers in a mirror world before bringing Shizuka Minamoto to join the fun. The trio enjoy but later however, Shizuka accidentally presses a button on the control panel that makes the robot fire a huge laser beam that destroys a whole skyscraper. The group realizes just how dangerous Zanda Claus really is, and they decide to return to the real world and forget about ever having found the robot. However, Nobita forgot about the sphere that has been sending telepathic messages to a mysterious girl named Lilulu. The actual owner of Zanda Claus, Lilulu seeks out Nobita when he accidentally lets slip all that he knows about the robot. After Lilulu proceeds to force him into showing her where it is, Nobita borrows the Roll-Up Fishing Hole from the spare pocket Doraemon keeps in the closet to take her to the World Inside the Mirror. She reclaims Zanda Claus while getting Nobita to let her borrow the Roll-Up Fishing Hole for a while.
After some time, Nobita is visibly nervous about what she is up to and, after seeing two shooting stars in a row, he uses the Bamboo Copter to investigate the forest at Mt. Ura. There, Nobita follows another shooting star through the unrolled Roll-Up Fishing Hole and finds Lilulu building a massive robot army. Doraemon, having been suspicious of Nobita’s peculiar behavior at home and having follows him there. They enter the mirror world and see a massive base being built by humanoid robots. The duo then use a long-range Paper Cup Phone to listen in on Lilulu as she orders the robots to work faster. She is revealed to be a human-hating robot. When Lilulu discovers them, Nobita and Doraemon escape to their own world with the portal accidentally destroyed by Zanda Claus.