Matsya: An Abandoned Prince

A marine world far away from Earth. More developed. And the evil mermen chose to invade Earth.
No one was more powerful than him in the whole mermaid world. The last one can evoke ancient magic, unlike others willing to kill people for a taste of magic. Still, he got backstabbed by his own, and Matsya's crown prince was abandoned vitriolic and lost.
He made the Alien planet EARTH his home. Humans accepted him and showered him with love. He fell in love with a human girl.
The fear of Marak starts looming over evil Mermaid Land. The planet is in grave danger. They know the secret to tackling Marak, but the corrupt generation wants EARTH rather than save their own.
Do the deities are so easy to fool?
Will the abandoned prince help the backstabbers?