During a forbidden excursion to see the surface world, a goldfish princess encounters a human boy named Sosuke, who gives her the name Ponyo. Ponyo longs to become human, and as her friendship with Sosuke grows, she becomes more humanlike. Ponyo's father brings her back to their ocean kingdom, but so strong is Ponyo's wish to live on the surface that she breaks free, and in the process, spills a collection of magical elixirs that endanger Sosuke's village.

In Italy in the 1930s, sky pirates in biplanes terrorize wealthy cruise ships as they sail the Adriatic Sea. The only pilot brave enough to stop the scourge is the mysterious Porco Rosso (Shuichiro Moriyama), a former World War I flying ace who was somehow turned into a pig during the war. As he prepares to battle the pirate crew's American ace, Porco Rosso enlists the help of spunky girl mechanic Fio Piccolo (Akemi Okamura) and his longtime friend Madame Gina (Tokiko Kato).