It-...there's an illness, where we come from. Daemons are the end result of being infected by it--humans become bloodthirsty monsters in varying shapes. They can no longer exist in sunlight and live only to attack and infect others. It's far from a pleasant fate, and daemons themselves are an everpresent threat out in the wilderness after dark.

...At least they were. I imagine there are better ways to drive them off in current times. [you know. lights.]