I'd be interested in several of those fandoms. So long as OC's are okay.
Halo
Star Wars- Don't worry I'm not obsessed with being a Jedi... I just like their powers. Otherwise Jedi are boring.
Rosario+Vampire
Dragonball Z: I wouldn't be a Saiyan as they are cliche... I'd be an Android similar to 18.
Starcraft: So much I'd want to do.
Fairy Tail: Lots of ideas... so far as unique magic goes.
Might do Assassins Creed but not sure.