
How is he preying??? So far he's not being aggressive(doesn't hurt him), doesn't demand anything from the merman, he's not manipulating him or deceiving him, and the merman is as free as a bird, this means that he can depend on others as well since he is not in any way shape or form restricted from communicating w anyone. Would u rather he stay at the aquarium devoid of any knowledge? Which do you think is the predatory relationship

“Child like teen” both of those are wrong. He’s a grown man, as mentioned. And his so called “child like” attitude comes from not knowing anything about the culture he’s in. If a young adult moved to a different country and didn’t speak the language or know the customs, they’d be innocent clueless as well.

19 year olds are not adults. They are adolescents. They are neither kids not adults. They are in a transitionary period with more responsibilities put on them which makes most very unstable wisdom wise.
In this specific case he has a child like mentality towards human culture. He was sheltered all his life, and is going to rely on the TEACHER to acquire that information. The teacher already has romantic inclinations towards and is going to be his guardian of sorts. If the teacher was not taken in by the beauty and has a crush and took charge of the mermaid then it could be an innocent relationship as you stated.
Also, if a teacher or other adults with power of authority or influence over the young adult in a different country approached them with romantic intentions, I would still considered that as preying.
So a 24 year old TEACHER is taking the guardianship of a 19 year old who he is interested in romantically? Moreover the 19 year old is quite child like and was sheltered?
This to me, SCREAMS grooming and pedophilia. What is with this disgusting trend of stories with pedophilia and grooming these days.