Eri Saito

As one of the seven mermaid princesses, Lucia must travel to the human world to protect the mermaid kingdoms.

Iwaki Tomonori is a schoolboy who happens to have a crush on his teacher, but learns she has become engaged. Brokenhearted, he soon meets a girl named Rizel, a biochemically engineered human, who he learns the Japanese government has married him to against his will.