Five-year-old Zongsuke lives with his mother Risa on a cliff in a small village near the sea. As the captain's father, he went to sea for many years, leaving Sosuke and his mother to depend on each other. Therefore, the five-year-old Zongjie has been over-aged and sensible since he was a child, and he also knew that he had to take on the responsibilities of the family and take care of his mother in place of his father. One day when he was playing on the rocky beach under the cliff, he picked up a mermaid Ponyo whose head was trapped in a glass bottle. Sosuke rescued Ponyo and kept her in a green plastic bucket.
Ponyo and Sosuke are fascinated by each other. Zongsuke said to Ponyo: "Don't worry, I will protect you and take good care of you." But Ponyo's father, the magician Fujimoto, forced Ponyo to go back to the sea with him. Ponyo resolutely refused and began to make a big noise. She was determined to become a little human girl and return to Zongjie's side, so Ponyo decided to run away from home. Just before she left home, Ponyo poured her father's most treasured "water of life" into the sea. This action caused great turmoil, the sea level began to rise rapidly, Poniu’s sisters turned into huge fish-shaped waves and swallowed the town where Zongjie lived, and almost even the home on the cliff of Zongjie Mountain was affected.
