Doraemon: Nobita's Great Battle of the Mermaid King

Nobita asks Doraemon to take him somewhere they can go diving, so the robot cat uses a few gadgets to create an imaginary ocean in the sky where they can swim. When they turn off the illusion, a mermaid named Sophia accidentally ends up in Nobita's backyard. She reveals she’s a princess from an ancient underwater civilization. Doraemon, Nobita, Shizuka, Jyaian, and Suneo quickly befriend her and are invited to visit her homeland. On their way to the underwater kingdom, they stumble into a long-standing conflict between the mermaids and a rival tribe that forced them from their home planet centuries ago. Now, Doraemon, Nobita, and their friends must help Sophia find a legendary sword that could finally bring peace back to the ocean.