We saw a short film called "Mermaid" last week.
The characters were a boy, a fish, and a mermaid, and the story took place mostly by the ocean and the boy's house.
When the boy was looking at one fish, he starts imagining that it is a mermaid. His imagination gets bigger and bigger, so he takes the mermaid home and puts her in his fish tank to let his parents see her. When the boy points at the mermaid, his parents only see a fish. Since his country restricts imagination, he gets punished.
At the end, I think I saw both of them swimming together, so I think the boy himself will turn into a mermaid and live in the mermaid world forever.
I think Tezuka wanted us to not stop imagining things and keep dreaming.
I also want to answer Kaho's question.
I love imagining things (in other words, "Mousou") too, so I think I can't stand living in that country. If I was in the boy's situation, though, I would keep my imagination to myself because I don't want to be kicked out of my country.