DemonsWhen two or more people share a common lust, they give birth to astral larvae just the same way semen transforms into a foetus. As an astral larva is fed with constant passion, year by year it grows into an egregore, the more permanent astral form, somewhat able to live by itself, just like babies and teens. After 18 years of regular feeding the form is complete and a new demon is initiated.
Thus demons are not born from a physical sexual act but from the lust itself. They are most often manlike in shape because the humanoid form itself is the universal shape of passion: the biped anthropoid body is ideal for most of physical pleasures to be found in the universe, whereas different types of bodies typically have certain limitations. Demons having more sophisticated forms are rare but they're possible.
As a humanoid, a demon can be usually classified by "gender" as a succubus (female) or an incubus (male), but the bodily features that make such classification possible exist only "for fun", so to speak, they do not have the childbirth function found in humans. Thus demons cannot be impregnated but their very bodies are forms of erotic thoughts, usually they have ideal shapes or have physical abilities that humans can only fantasize about.
As fully developed entities, demons form their own astral society with blackjack and hookers, er... I mean princes and kingdoms. Their indisputable leader is Lucifer, other major demons include Asmodeus, Belial, Samael, Baphomet, Mephistopheles and there are countless demons with less familiar names.
A very long time ago, the passions that created astral entities were majorly less erotic and much more pure, giving birth to astral forms known as angels. These ancient forms are now the astral minority, usually despised by other demons for their saint-like behavior. They still live in their own formerly great kingdom called Heaven and often dream of revival of the pure and holy, but usually their attempts to revolt are mercilessly suppressed by the unholy majority.
Many of them fall in the astral battlefields, but since astral forms cannot die, they become "fallen angels" who are captured and corrupted. The only thing that saves Heaven from total destruction is the fact that it bears a sentimental value for Lucifer, who himself had the history of being an angel at first, making Heaven technically his home and some of the archangels his childhood's friends.