Since in the country I come from (Italy) I've the hardest time finding a site like this to post extract from my original works and get them reviewed, I thought I'd try and write a fanfic. It was actually a lot easier finding a nice site to post it to. But I'm unsure on how you actually go and write a fanfic. Let's say I have a nebulous idea of what a fanfic is, but I'm unsure on how I should treat characters, situations and locations and blend them with a storyline which is my own. And make it NOT a plagiarism. Since it's a fanfic, I suppose it's a given that you're using someone else's characters. But how should I go about describing/using them? Should I keep the originals as they are? Or am I allowed to change them a little, like keeping the name but changing the surname, or changing their background while keeping their general appearance/attitude? Next, situations. Am I allowed to re-elaborate a situation from the original work I based my own from, or to make, like a quotation? Or is that plagiarism? What if I insert in my piece of writing a situation that's slightly different from the original but it still refers to it? And what about locations? If I locate my story in THE SAME WORLD as the original story took place, is that plagiarism, too? And if I'm writing a crossover + alternate universe piece, am I allowed to use the characters freely? Or are there restrictions or something? I also wanted to ask about original characters, that is, characters that are my own and are inserted in the flow of the story alongside characters I picked from the work/works I'm basing my own from. Can I do that?