So, I've been playing around with Perchance some more. And I discovered something.
Perchance, at least with the generator I used, "Image Generator Professional," doesn't know about Frieren if you name her. If you say "I want an image of Frieren in a pretty sundress," it gives you a generic animoo girl. But if you describe her: "short petite Elf woman, pale green eyes, silver hair, pigtails, wearing striped blouse, gold and white cloak, and black leggings," it immediately renders images of perfect Frierens (Frierenen?), with lots of little details, like her earrings, which I did not mention in the prompt, exactly like in the Chinese cartoon. Not every detail is always exactly the same but it's always definitely her, very recognizable. Usually when you're trying for a character an AI doesn't recognize, you have to do a very long, detailed prompt, and run dozens if not hundreds of iterations to pick out a few where there is a resemblance.
I am trying to figure out what this means. Is the AI using a model that has Autism Elf waifu art in it, just not tagged with that name? What other characters are in there? I've been trying for Marcile from Dungeon Meshi but not having much luck so far.