If you loved Doraemon: Nobita and the Island of Miracles – Animal Adventure, try Doraemon: Nobita's Great Battle of the Mermaid King
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.
You already loved

Doraemon: Nobita and the Island of Miracles – Animal Adventure
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Doraemon: Nobita's Great Battle of the Mermaid King
What they share
Both films are directed by Kōzō Kusuba, and they both carry the cozy, playful mood tags, and they sit in Adventure / Animation / Family / Fantasy / Science Fiction territory. If that's the register that drew you to Doraemon: Nobita and the Island of Miracles – Animal Adventure, the second film will land in a comparable space — through a different lens.
cozyplayful
What Doraemon: Nobita's Great Battle of the Mermaid King is
Apparently someone needs to save an underwater kingdom. Nobita and friends help mermaid princess Sophia. It involves a sword from another planet somehow.