Read Merin the Mermaid hentai manga on hentaidexy.
summary for Merin the Mermaid :
Mermaid are mythical creatures who seduce humans with their sweet voices and beauty in order to feed on their hearts. But Dee, a mermaid, fell in love with Lewen, the prince of Erenbur. She was unable to eat his heart. Instead she loses her voice in exchange for legs to live on land and reunite with the prince. Meanwhile, the elder prince Lewinel returns home with his newly betrothed Irena, the princess of Ladivita.