When Nobita goes diving with Doraemon, a mermaid named Sophia comes close to him and they all befriend her. When they proceed towards her kingdom, they encounter a fight between two opposing tribes.
Doraemon: Nobita's Great Battle of the Mermaid King is a 2010 Japanese animated science fantasy action adventure film based on the manga and anime series Doraemon, and is the 30th Doraemon film. The film was released in Japan on March 6, 2010.