My guess, an Inu Yasha fanfic.
And sorry, but I don't think we can help you... Pondering on ideas for other people is not usually what writers do. My guess is, watch some episodes of IY, and pay attention to detail. Can you see a mysterious sub plot on which you can build on? Or mayhaps a mysterious character you think you can make more important than he/she is.
Other than giving you this advice, I can't help you. I've never seen a full episode of Inu Yasha. wink