For us that meant the design grid said Aeron, god of murder -> dominion of the body -> ? Civilization.
It was actually a very easy decision, as I mentioned it was the first civ we picked. But Aeron was cruel and calculating, methodical and powerful. Not overt like Camulous, not involved in massive wars, he comes for you from the shadows, he is the god of assassins. So these are a dark, subtely powerful people. Body gives us blood, passion (but not ideological like Bhall, more base) and flesh. Because they epitomize body magic they should be perfect of form and beautiful, and because they epitomize Aeron they should be swift, strong and cruel.
Vampires were the perfect choice. But the design grid lead us to a specific implementation for them which became the Calabim. They are alive because they represent body magic, they are driven by the desires of the flesh because of this, they are cruel and punishing because of Aeron.
Hope that helps.