Domain Of Dragons
In the days before Tiamat and Bahamut came into their power, no dragon ever died. Beasts and men passed from the world, returned to Io, and were reborn; but dragons were immortal. When Io was lost, things changed.
The mortality of his dragon children disturbed Bahamut. When the children of Io die, the energy in their souls returns to Io, is cleansed, and is reborn into the world. The life energy of dragons seemed simply to vanish. This loss of energy was abhorrent to Bahamut.
Bahamut believed that dragons lacked some element that tied them to the earth. Without this important tether their souls simply evaporated upon death. He and the sentient creatures under his sway went to work, attempting to isolate this key element. Using great magical power Bahamut and his alchemists split apart and recombined Io’s creations, merging beast, sentient, and dragon it varying proportions.
Some of the creatures created this way were monstrous or mad. Others were pathetic and pitiable. Failures were sentenced to death. But many escaped, going on to populate the Feywild. When Bahamut was sure that he had isolated the tether, he chose what he believed to be his ten finest creations and fused them to the ten breeds of dragons. These servitor races would attend the dragons in life and bring their souls to him in death.
Unfortunately, Bahamut was mistaken. The demihuman races he gifted to dragons can serve them in life, but do not have the power to prevent the dissipation of their souls. This fact torments Bahamut, still.