Succubae and incubi are easily the most common type of lesser daedra, and probably the most common type of outsider.1 An incubus is male and a succubus is female, but their general purposes are the same: to seduce mortals into having sex with them, thus draining a good portion of the mortal's energy (and enjoying themselves greatly in the process). This is how incubi and succubae feed, and when Suspira is nearby they channel a portion of that energy to their Mistress. Incubi and succubae need to feed at least once a week, though they will do so much more often if the opportunity presents itself.
These daedra can be potent undercover weapons (no pun intended): they can take on virtually any form, have an intense personal magnetism, and know every trick of seduction in the book. If one of these daedra sates itself on a single human being, that person will be drained, catatonic and useless for the next twenty-four hours. While this can be useful at times, however, it runs the risk of exposing the daedra's true nature, which can be harmful if the daedra needs to stay in the same place for a long time. Many incubi and succubae, realizing this, have taken to "snacking" on smaller doses of energy on a nightly basis, allowing their partners to remain functional the next day. Others conspire to produce orgies instead of one-on-one encounters; this allows them to take a smaller measure of energy from each participant while still being fully sated themselves.2
Impregnation is virtually guaranteed with these creatures, unless magical contraception is used.3 A succubus impregnated by human males will give birth to a fairly ordinary child with little or no supernatural power, which appears human if raised on Earth, or resembles an adult succubus's "natural" form if raised in the outer planes. Upon reaching adolescence the child is transformed into a full-fledged incubus or succubus, and must begin feeding on sexual energy in order to survive. This is the primary (and perhaps only) method by which these daedra reproduce; it is believed that incubi and succubae are unable to draw energy from each other, and thus will mate only with mortals.
Since daedra will not die of natural causes (though they can be killed when in their corporeal forms), and the incubi and succubae are both very fertile and very promiscuous, the numbers of these creatures are growing every year — much to Suspira's delight.
A succubus in its natural form resembles a very attactive human with reddish skin, red or yellow eyes, black hair, a prehensile pointed tail, batlike wings, and short, stubby horns protruding from the upper corners of the forehead.4 In this form they are often mistaken for tieflings.5 However, these daedra are consummate shapeshifters and can take on any humanoid form, maintaining it indefinitely; because of this, many of them masquerade as human while on the Material Plane. Succubae can have sex in male form and incubi in female form; they are only fertile when in their native genders, but they can draw energy from their partners regardless of the genders of the participants.
Incubi, Succubae, and Mortal Souls
Because incubi and succubae are always half-human (or half-mortal, anyway), they have a mortal soul in addition to their daedric Essence. This means that incubi and succubae have two things that other lesser daedra do not have: the capacity for free will, and the ability to develop a conscience. It is rare for their human sense of morality to survive the transition from childhood into their mature daedric form, but it is possible for an incubus or succubus to rekindle its lost humanity, particularly if it forms a bond with a mortal who can "remind" the daedra's soul of its true nature.
It is also possible for a teenage incubus or succubus to be purged of most of its daedric essence, if its true nature can be discovered before it completes its metamorphosis into an adult daedra. The ritual to do this is very difficult, not to mention painful for the subject — but if it is successful, the subject will become a tiefling, with only minor signs of his/her daedra heritage, and his/her human personality will remain intact. There may not be any outward signs if the ritual fails, particularly if the daedra is clever enough to disguise itself as a tiefling and thus appear "cured".