Manga or anime movie - 80's or 90's
My question is concerning a movie that could very well be a Manga or anime full length film. I had to of been about 8-10 years old (in my early 20s now)
It was a cartoon for sure.
It was about a young boy who lived under water and was in love with a princess (I think) and he couldn't be with her because he lived underwater.
The boy was friends with a little mermaid fish. Who had a horn coming out of it's forehead. I remember at the end of the movie this little one get severely hurt because of rocks falling I believe.
Please help all you movie gurus!! I'm driving myself crazy!