Board Thread:Questions and Answers/@comment-72.64.15.52-20171014132337/@comment-25047329-20171014190937

The tropes Ishida uses in themselves are pretty common, but the specific ways in which he portrays them are his own. Stuff like "flesh eating humanoids with superhuman abilities" and "shapeshifter weapons" aren't unique. You're free to use those ideas in broad strokes. Terms like "kagune" and "Rc Cells" and the finer details behind them are unique to TG and you can't use them in their entirety.

"Ghouls" are a generic monster like vampires and werewolves. There's no copyright for them. The ghouls in TG are Ishida's specific interpretation. You can have ghouls in your story, but not Ishida's interpretation.

I suggest just looking around and doing some research into flesh eating monsters in folklore. Maybe take some inspiration and create your own thing.