Everything. Although the plot doesn't fluctuate from Tsukiyo's writing, I made sure to fix all the plotholes he left, give depth to characters, who, in the original, were nothing but skyrim followers with sexlab for Keyaruga, and even add a lot of my own stuff, starting with extensive descriptions in the text.
Would this get expunged? I didn't read it, but based on the description, this would be considered a doujin. Don't know which rules it would violate. Novel's aren't against the rules as far as I know. As for doujins using artwork from other sources, this wouldn't be the first on this site. At worst, this would just be considered a "bad translation". Unless the content that does exist in the original is taken word for word, then maybe...