Doraemon and friends trying to save a boy name Kukuru and his tribe from Gigazombie who want to change history for his own sake in the ancient times.

When Nobita feels like diving in his hometown, Doraemon uses a Underwater Pump Simulator to pump all the water out of Tokyo, causing the entire city to go underwater. That night, Doraemon and Nobita use a Diving Mask Simulator to dive underwater. Later on, lots of fish, and a shark attack Doraemon and Nobita. So, Doraemon puts a stop on the Underwater Pump Simulator, but there is a girl named Sophia, lying down on the bushes in his neighborhood.

The film starts with Gian seeing some like spirit and it asks him to accomplish a task. The story starts when a stray dogs are searching some foods in the can. Then a dirty white dog comes out of nowhere. Just then, the dog creates a close stare to the stray dogs and forces to run away. But the dog is disappointed that he doesn't know what to do after searching the garbage, under the pouring rain. After that, Suneo starts saying about the discoverable places on Earth and him and Gian are totally disappointed about that. That then, they are asking favor to Nobita to take them to an undiscovered place to be seen by their naked eyes. Nobita refuses but tells he will try his best. He comes to upstairs to explain Doraemon what the problem is now.