How about a bounty hunter comes to Earth for Zim?
Or maybe Zim and Dib travel to the Massive to defeat the Tallest!
Or perhaps you could have them attempt to conquer the Earth.
Or you could just make it an old school "Hi Skool" romance. ^w^
Why thank you, but this topic is OLD. They are nice ideas. I'm going for the last one with a little Invader Zim and EMO in the mix. I've already written out the rest of the story though. Still, I like hearing ideas.