Ningyo Oujisama (Mermaid Prince, 人魚王子さま) by Yuana Kazumi is a Japanese manga published by Zenon comics. So far, three volumes have been published.
A mermaid wants to become human to be with a guy she thinks she loves. She is accidentally aided in her quest by a different guy, a gambler. (At first, said gambler wants to take her picture to make some money, but circumstances change his mind.) The mermaid and gambler both make sacrifices to fulfill her wish . . .