does the fanfic hav 2 b about a certain thing?

in the fanfic comp, does the fanfic hav 2 b under a certain category? e.g. you hav 2 write a fanfic 2 do with aliens.
cuz that would b cool. and it would make the comp more interesting. it would also make it easier 2 judge the fanfics cuz they would b the same theme.