The son of a sailor, 5-year-old Sosuke, lives a quiet life on an oceanside cliff with his mother Lisa. One fateful day, he finds a beautiful goldfish trapped in a bottle on the beach and upon rescuing her, names her Ponyo. But she is no ordinary goldfish.
When Sophie, a shy young woman, is cursed with an old body by a spiteful witch, her only chance of breaking the spell lies with a self-indulgent yet insecure young wizard and his companions in his legged, walking castle.