The latest animation from the Japanese master, Hayao Miyazaki. It's been slightly Americanized by the good folks at Disney: voices performed by people like Tina Fey, Cate Blanchett and Betty White.
Ponyo is a fish, or at least she starts out that way. Posessed of an independent streak, she sets out to explore the world without the permission of her dad, the once-human wizard Fujimoto. (Yeah, I'm not sure how that works either.) She immediately gets in trouble, trapped in a jar; she's rescued by 5-year-old Sosuke. They quickly establish a bond, and Ponyo resolves to become human and stay on land.
The magic she requires to do that, however, sets Mother Nature seriously out of whack. We're talking storms, floods, the Moon falling out of orbit. It takes a good deal of heroism on Sosuke's part to resolve things.
As usual with Miyazaki, all this is played out with fantastic style and sly humor. My descriptive skills are lacking, because just about everything I can think of sounds like a cliché: "a feast for the eyes"; "visually breathtaking"; … Just go ahead and get it.