It's always been hinted that there is a deep-seeded hatred between the Pegasi that guard Princess Celestia during the day, and the bat ponies that watch over Princess Luna. The two species have had a very fragile peace between each other, but what would happen if that was shattered? And what would it take?
I really don't have a plot developed, mind you, but I thought it'd be interesting if the rivalry came into true war-like fruition. Or, at least have there be some sort of competition to show which species is truly superior.
I don't know. I just want to use my bat pony. -.-