Excellent litfic for those who can stomach body horror. 
As a former swimmer, this one cut a little close. I loved the way the story was told with mermaid Ren and epistolary Cathy. Poor Cathy, Ren didn't deserve Cathy. 

Ren's breakdown after the DQ was hard to read. I was thoroughly disturbed by Ren's tail. I was expecting a different kind of body horror lol.

 
Overall, this made me very sad.