This is something I read a while ago, so my memory is not the clearest.

It opens with a girl realising that she's somehow wandered into the spirit world. She is soon captured by some spirits who sell her to a slave auction, where she's bought by a brothel that forces her to work as a prostitute.

I have a few more memories of the story, but I've reached the point of my search where I have 200 tabs open, none of them are what I'm looking for, and I've gaslit myself into doubting that the story even exists. The only other detail that I can confidently add is that it is NOT Minikui Yuukaku no Ko. It seems to have almost the exact same plot setup, but it isn't the one I'm looking for (although I'm reading it now, because why not :P )

While I'm here, if you have any other 'spirited away' type stories, feel free to suggest them. I'm in the mood for weird-otherworld stories, and I might as well cast as wide a net as possible :)