First, take a deep breath and don't panic! That's the key.
What I tend to do, as I don't do 'straight' human stuff, for the most part, is turn them into some kind of shifter. I think they're more interesting. I also tend to make up critters (have a hellcat going as one for something right now and it's a creature). However, unlike this 'verse, you should probably make it critters you don't have to explain a lot as people have some knowledge going in. It's easier than people throwing fits over it with you. I didn't have much of a problem with the two Inuyasha fanfics I published, but they were shorties and AU. Then just go how you want with it, just avoid too much that is easily identifiable canon.
Below are the links to the two of mine.
www.amazon.com/Shifter-Tales-There-Riding-Stormy-ebook/dp/B007GDUWZW/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1436915491&sr=1-1
The one in Shifter Tales that was IY was It Was A Dark and Stormy Night --it was a Kagome/Inupapa story
www.amazon.com/Eyes-Shut-Shorts-Danyealle-Autumn-ebook/dp/B0074N67DU/ref=sr_1_4?s=digital-text&ie=UTF8&qid=1436915491&sr=1-4 this was my entry in R0o's first GM challenge
Any questions, feel free to ask either here or via PM