Merworld

"I consider myself a reasonable merman," Triton thundered, "but contact between the merworld and the human world is strictly forbidden. Why did you disobey me and rescue that human?"

Oliver hadn't written any stories about the merworld, but knowing him there were probably at least a couple pages of notes about the place somewhere in his notebook.

Reflecting a slightly modified version of the hero narrative, Eric rescues Ariel from Ursula and concomitantly saves the merworld from a diabolical female in lieu of a male villain.