Man, that’s a classic question that pops up every now and then. I used to assume it was from a manga, maybe because the richness of the world felt like it could only come from a long-running series. But nope, it’s an original screenplay by Hayao Miyazaki. He started developing it after conversations with a friend who runs a summer cabin for young girls, which eventually evolved into Chihiro's story.
It makes sense when you think about it. The episodic nature of her working in the bathhouse, meeting all these strange spirits—it’s structured like a folktale being told on the fly, not like a straight adaptation of existing panels. You can see Miyazaki’s usual themes of environmentalism and a child’s resilience, which are pure Studio Ghibli. There’s a collection called 'The Art of Spirited Away' that’s fantastic, but it’s art and commentary, not a source novel.
Honestly, I think the myth persists because the world feels so fully realized, like it should have a book series. It doesn’t, but that almost makes it cooler—it’s a complete vision from one mind.