This story takes place in a country where it is not allowed to imagine freely. The main characters are a boy and a fish which the boy thinks is a mermaid. The boy falls in love with his imaginative mermaid. However, following the law of that country, he gets arrested and taken away his ability to imagine. The climax of this story is when he got his ability to imagine again and dives into the ocean with the mermaid.
I think that what Osamu Tezuka wanted tell us is that nobody is able to interfere with your inner thought.
