i wish i saw more representation of that in fiction. the way you describe the brainfog is poetry. imagine getting to cuddle / molest a wispy, deathly thin cutie who is barely mentally present but feels nice...
I added more little notes of prose in the CoC1 mod for having no thickness and no tone, and even went as far as making a parser tag for it so I could more easily write [if (isemaciatedbuild)] instead of doing two stat checks (among other body types like isskinny, isfat, ischubby, etc.)
It's not lich queen really but in the glacial rift you can find a bony emaciated category of demons I called moras. Or "weeping willows" if you want to get poetic. You might like them, but they're a total dead fish when it comes to sex.
The gilts in the volcanic crag have extremely lean bodies with practically no fat, but they're firmer and quite preppy. And their ribs are hidden by the armor hooked onto their flat chests. But a deep well between those hips!
That's probably all I've added for people seeking bony girls. I had some interest and wrote a few thousand words of a possible [Lover] that would be all one huge allegory for anorexia, but that was less her being anorexic and more your relationship to her being a person's relationship with their anorexia. Except you get ice magic out of it.
Was fun to work on, but too spontaneous(I was home with a fever and just woke up from a nap and started going at it like crazy) and not really right, so I threw that one away. Ideally the mechanics and her charisma would make it so you want to walk into the danger of it thinking you can just cut things off when you got all your spells but the journey there, and what that leaves you at, makes it a lot harder to turn back. Fits the broad theme of corruption, but I think it was just too out-there and wasn't really clicking.