The Mermaid Sex Slave Game Over is an ending which occurs if the party loses a fight in Return to Mermaid Caves against any enemy except the Nereid.
Greeted to another day by the Mermaid Princess, but Eric(a) was too broken to even finish a sentence without breaking into tears. The princess has subjected them to such conditioning that they not only enjoy being used as a sex toy, but couldn't remember their name as well. Even worse, their hatred for their current captor is slowly fading away, the joy of being given a new name by the princess makes them feel sick to the stomach. Given the task of pleasuring the council alongside the mindbroken Pussylicker or be placed as public sex slaves or even worse punishments, Eric(a)'s story ends on a tragic note.
Maybe one day Marianne will rescue the Cutie Knights and restore their broken minds, but that is the story for another day.