In a devil's story that is at least partially true, it is said that in the time during the war over Ys-Pravi where she was split in two by her lovers, Koss was overworked repairing Throne and broken tools of war.
Koss took the cool white flame from the fingernail of the smoldering corpse of UN, and worked it for a year and a day. When it was to his liking, he took his bronze chisel and split it into various orders of servant to perform tasks around his workshop and Throne. To quash their rebellious nature, the Angels were crafted.
Servants and humans can all do the same things, the difference is primarily that servants are immortal unless killed, and humans naturally age and die. Servants also are bound by their proclivity for whatever their race was forged for, so humans tend to have a stronger will and potential for power.
Servants do reproduce, but their rate of reproduction is much, much slower than humans. There are a few races created for dangerous jobs, such as Goblins, which had a high breeding rate, but still retain the natural unlimited lifespan of all servants. This has created a population glut of those races and led to their dominance in Throne guild life.
Servants can and have created pacts with devils, but they are more stable than pacts with humans, so devils are usually reluctant to enter into them.
- In an earlier version of the story, the servants were the "Black Sons of UN", but this idea was scrapped for the current idea of the cool white flame.