I agree with kidd, the most pitiful character is Mau Dan. She loves Roger very much and at first the mermaid is trying to help both of them to be together, so she set them up a nice house away from everybody.
Mau Dan is prettier than the mermaid. In reality, Mau Dan's body is dead but the mermaid (Yuki) went into her body making Roger thinks that she is still alive. Eventually, the mermaid fell in love with Roger.
I love the theme songs... all were sang by Yuki Hsu (the mermaid).