A lot of people worldbuild when they daydream and have the bones of a story kicking around in their brain, but have to pay the bills and raise the kids etc so they never flesh it out and write it down. What’s your story’s premise? Fantasy, sci-fi, alternate history, mystery, western, whatever genre.
A doppelganger of sorts replaces a character, but it’s entirely for the better. Despite being an unearthly monstrosity, it’s well meaning, good intentioned and has everyone’s best in mind. Unfortunately this isn’t seen as a good thing by the crowd the original ran with, and those who find out are at a crux between liking the person and fearing the monster.
This is a Star trek Voyager episode. Can’t remember which one.