One day, the boy helps the fish and it turns to a mermaid. The boy and mermaid play together in the ocean and have a lot of fun. At the end of the day, the boy brings back the mermaid and introduce her to his parents. However, the mermaid is just a normal fish to other people, so parents send the boy to a government's institute, saying their son have lost his mind. There, he was treated horribly to forget about the mermaid. Few days later, the boy escaped out of the laboratory and released the fish back to the ocean, and again the boy sees the mermaid and swam away together.
I believe that at the end of the story the boy change himself into a mermaid or fish, so that he could live together with his only and beloved friend.
