Somebodys infringing on my fanfic! What can I do, legally?
Damn little, if it includes any characters or elements that are not original. While it’s easily permissible to create fan fiction, you’re not going to have any success in copyrighting it. In this situation, good luck. Of course, infringing on somebody else’s fanfiction idea (in this case, we’re referring to outright plagiarism, or writing under the aegis of somebody else’s series) is considered very dirty pool; check the “ethics” section.