Doraemon Movie 04: Nobita and the Castle of the Undersea Devil

The Doraemon Movie 04: Nobita and the Castle of the Undersea Devil takes place during Nobita's summer vacation, which he spends under the Pacific Ocean with his friends. While exploring the Atlantic with Doraemon's underwater vehicle, Jaian and Suneo discover they're running low on energy for the environment gun, making them vulnerable to the sea. They're rescued by creatures from the underwater kingdom of Mu, who capture Doraemon and his friends, revealing their true intentions.