Sakana to Mizu no Mori

Van is a mermaid who has lost everything—his voice, his family, his very place in the world. Forced to work as a slave in a mansion located in a town by the sea, he dreams of the day when he can return to the water. One day he meets Jens, the sole inhabitant of the cursed island of Fiska, a young man who proves to be kinder than any human Van has ever met. As the two grow closer, Jens is determined to buy Van's freedom and bring him to his island home. But in order for this to happen, Van and Jens need to become more than just good friends...they need to fall in love.

(Source: Seven Seas Entertainment)