The film was released in Japan on July 19, 2008, and it has won several awards, including the Japan Academy Prize for Animation of the Year.
The plot follows Brunhilde, a fish-girl who lives with her father Fujimoto, a once-human wizard or scientist who now lives underwater, and her numerous smaller sisters. One day, while she and her siblings are on an outing with their father in his four-flippered submarine, Brunhilde sneaks off and floats away on the back of a jellyfish. After an encounter with a fishing trawler (the net of which is scraping the trash-strewn bottom of the harbor), she ends up stuck in a bottle. She drifts to the shore of a small fishing town and is found and rescued by a small boy named Sousuke. Splitting the bottle open, Sousuke cuts his finger in the process. Brunhilde licks his wound when he picks her up, and the wound heals almost instantly. After taking a great liking to her, Sousuke renames her Ponyo and promises to protect her forever. Meanwhile, a distraught Fujimoto is searching frantically for his daughter. Because of his own bad memories of the human world, he believes that Sousuke has kidnapped her, and he calls his wave spirits to recover her.
And that's it for the spoiler! :D It is quite an enjoyable movie so I recommend you to watch it!
For now, enjoy the trailer below!