The cast of Ponyo included well-known actors and actresses, such as Liam Neeson, Matt Damon, Tina Fey, Cate Blanchett, Lily Tomlin, Betty White, Cloris Leachman, plus Frankie Jonas (the younger brother to the members of the musical group the Jonas Brothers) and Noah Cyrus (the youngest daughter to Billy Ray Cyrus). None of the characters played by these actors were expendable to this story.
To summarize, this young boy named Sosuke, who lives by the sea with his mother and father (a ship captain), rescues a goldfish whom he names Ponyo. This goldfish was magical and could do things like heal a cut by licking it. Having tasted human blood, Ponyo started turning into a human girl, something her heart desired very much. As a result the world became increasingly out of balance with the moon nearing the earth and causing tsunami size waves. You will have to watch the movie to find out what happens in the end and how the balance to the world is restored.
Take a minute to watch this clip from the film showing Ponyo on her first day as a girl:
Because this movie was set by the sea, the opportunities to create drama with animation using the waves, underwater creatures, and stormy weather was quite extensive. As you can see from the above video, the characters of Sosuke and Ponyo are so very endearing. Even though our 3yr old twins may not have been able to follow the storyline completely, they were still enthralled right along with our 6yr old son, who could not take his eyes off the screen because of these two characters and the dynamic animation.