Doraemon: Nobita's Great Battle of the Mermaid King

Nobita asks Doraemon to take him somewhere they can go diving, so the robotic cat uses his gadgets to create an illusionary ocean above the ground 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 befriend her and are invited to visit her kingdom. However, on their way there, they discover a long-running 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 to the seas.