Character
A boy, mermaid( actually a fish), the government
Setting
This story reflects the mood of the 1960s. In those days, people's right to think and speak freely were deprived by the government.
What do the characters want and the conflict
The boy just wants to daydream, but the government won't allow it.
Ending
The boy escapes from the government and takes the fish to the sea. He was so depressed because he couldn't see the fish as a mermaid anymore. However, as he was staring at the fish, his imagination came back and at last, he turned to the mermaid as well, and the two mermaids jumped into the sea.
What happens next?
I think the last scene is symbolic, and that it implies the boy could somehow escape from the governments' oppression. He might start acting to free people from the government's suppression.
Theme
I thonk that probably Tezuka Osamu wanted to criticize the government or maybe the whole mood of the period.
