How about instead of a sword fight, the aliens possess certain humans, and these humans must choose to either be possessed by them and in return they get special powers on earth or they must face a spiritual battle within themselves. This could manifest as mental illness perhaps.
These powers that the aliens give humans are like vampire powers maybe, or maybe they just become very successful materially. So, for example, let's say an alien possesses a human and gives him extraordinary musical talent but in return he must forgo God and reject all the transcendental characteristics of the good gods. haha
People are really into vampires right now, so I thought it would be a good idea to create a daemon/genie spin on it.
Here is a theme song for this idea:
[youtube]http://www.youtube.com/watch?v=xFDXSGZ7r_k[/youtube]
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As long as man continues to be the ruthless destroyer of lower living beings he will never know health or peace. For as long as men massacre animals, they will kill each other.
-Pythagoras