I thought the Mermaid story is similar to a movie called A Clockwork Orange.
1. Both boys were doing things that's illegal in each place. In Mermaid, it's imagining. In A Clockwork Orange, it's violence and drugs.
2. They both get torchered or in other words “a curing process” from the police.
3. In my opinion I think the boy in Mermaid committed suicide. The main character in A Clockwork Orange tried to commit suicide but he failed. I think they both couldn't run away from their beliefs.
Watching Mermaid I thought Tezuka Osamu wanted to show that imagination is a good thing. How I saw the story, I thought it's hard to change what you originally are. Not everyone will understand you. Mermaid felt really deep and dark for me. It might be because I thought about A Clockwork Orange so much. I wouldn't recommend A Clockwork Orange because it's really unappropriate but Mermaid really looked familiar. At the end, being yourself is a good thing but don't do violence and drugs or anything illegal. It will scar your life.