Which is why I said "you may not" be infringing. You CAN infringe, but there's no certainty that every fanfic, or even most fanfics, would be infringing on copyright. (TRADEMARK is a whole different matter. If you write a story with Captain Kirk in it, you've infringed on their trademark. In fact, I think *I* just infringed on it, because I didn't write Captain Kirk(TM Paramount) or whatever the proper usage is.