A form of magic, yes. A massive tree in the middle of their territory, which is slightly hollow inside and secretes a honey-like red substance collects the soul of one of these (as for now unnamed) creatures when they die and they're reborn in a different body as a different person entirely. But each one has a small hole in their chest as though their heart was ripped out. Because of this they need to find a human, and this hole fills in.
Recently I was inspired to come up with a race of 'perfect' males that appear otherwise due to their pointed ears, above-average height, and thin tails that lure and seduce rogues that become their personal supply of energy that ensure their immortality. And some become attached to their vessels and decide to go through a painful ritual that turns their vessels immortal as well.
I know a lot of mythical creatures as well, trust me. I'm just stupid sometimes... Although I do enjoy making up my own creatures for worlds of my own, know?
Ah! I remember now! /shot Good lord I swear, sometimes I'm just... I don't even know. Just take baby steps with me sometimes, Paps, I'm sure you know by now.
Ohh, fascinating... especially since incubi can't exactly control their outward ability. They simply exist and that alone can easily attract victims. Or whatever they want to use them for, anyway...