It's less guro and more like cronenbergian body horror transformation, but Horihone Saizou has a bunch of crazy stuff, a bizarre mix of horrifying and heartwarming.
It's so hard to find good loli erotica though, asstr is pretty much the only place that allows it, and searching for stuff there is a pain in the ass.
All I want is a good story about a loli being trained as a masochist slave from the start of her life onwards.