A whimsical undersea creature falls in love with a boy and uses her magical powers to become human, thereby upsetting the balance of nature. Japanese animation director Hayao Miyazaki’s riff on Hans Christian Andersen’s “The Little Mermaid” will surely please his admirers, as it exhibits many of his standard themes—childhood, magic, environmentalism—and the colorful grandiosity that is Miyazaki’s trademark. Those less enamored of Miyazaki’s work (Spirited Away, Princess Mononoke, etc.) will still find this one a harmless way to waste and hour and 45 minutes—decent enough family entertainment, though parents may find their smaller kids growing restless. For the U.S. release, Disney’s John Lasseter has assembled a celebrity voice cast (Tina Fey, Matt Damon, Cate Blanchett, Liam Neeson, etc.).