Watch Doraemon: Nobita's Great Battle of the Mermaid King - 2010

Storyline

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.