I haven't written fanfiction in a while, but when I do I think the thing I find most difficult is placing my character in the world - when writing an original one. I'll come up with back story to allow me to justify to myself that this character really belongs in the place I've put them (or at least, in the place they start from). This can be easier in Pokémon, where there already is an extensive world and story, but then that also adds to my 'placing' problem. Because I'll then stress not just about their physical place, but more their place as a person - as in their role and who they are. I want to avoid them being a clichéd character doing the same things other characters in the world have done time and again.