Doraemon: Nobita's Great Battle of the Mermaid King

In "Nobita's Great Battle of the Mermaid King" (2010), Doraemon and Nobita plunge into a submerged conflict where the aquatic realm of Princess Sophia teeters on the brink of destruction. Armed with a celestial sword from the distant planet Aqua, our heroes navigate treacherous waters to thwart an encroaching war, their mission a blend of aquatic adventure and fantastical weaponry that underscores the enduring charm of the Doraemon series.