I think that the main character is the boy, who believed mermaid was there. In the country boy lived, imagination was not allowed freely. He was reported to police by his parent, and they forced the boy to forget about the mermaid. The police tried to make boy to forget mermaid and when they knew that they can`t make him to, they put him in to jail until he can`t remember the mermaid again. What the boy did when he forgot mermaid was to go to ocean and throw himself to the ocean. What I think that Tezuka tried to do with this short animation is to sound the alarm to Japan, about neglecting the importance of imagination.
