Incubi are the best warriors in Dark Eldar society. They are warrior-mercenaries living only to kill. The Incubi's main job in Dark Eldar society is to act as bodyguards for the Archons or as enforcers. Many pleasure dens or smuggler's spires have been brutally destroyed by a host of Incubi just to send a message to their employer's rivals. The reason for the Incubi's use as bodyguards is that in Dark Eldar society, one's place in the chain of command is only improved by assassinating the person above you. Therefore, the majority of Kabal leaders find it too dangerous to leave the protecting of their lives in the hands of a member of the same Kabal, as the bodyguard would have ulterior motives for not sufficiently protecting the Archon. Incubi, on the other hand, are completely neutral in matters of Kabal hierarchy, follow the code of their contract and their Klaivex leader zealously, and are elite warriors, all of which make them perfect bodyguards.
Incubi, like Mandrakes or Haemonculi, do not swear allegiance to any specific Kabal or Wych Cult. Instead, Incubi are trained in their dark shrines. The smallest shrines have only a handful of Incubi, the larger ones are sprawling bastions full of howling marble statues with a central shrine where aspiring Incubi and other Dark Eldar come in their thousands to bargain for services or to join the order. As you can imagine from someone of the elites, training is extremely hard and gruelling. Due to this, not every aspirant survives the training. These weaklings are burnt as an offering to the iron statue of Khaine at the heart of each shrine making the Incubi metal as fuck and thus Awesome. The only way to stay alive is to quickly master everything taught. Should an aspirant live long enough to best a proven Incubus and take his armour, the final training will begin. Every aspirant must then kill an Aspect Warrior of the Eldar Craftworlds in single combat (mostly without the Aspect Warrior's consent), shatter their quarry's precious Soul Stone and rebuild it into a psychic torture device known as a Tormentor. After that, the aspirant can be considered an Incubus. Tl;dr: Incubi literally go Eldar hunting before turning their souls into torture devices so they can both violate their souls and their dead body. Again, considerations are made on why the Eldar still haven't cut off all contacts from the Dark Eldar, despite doing this shit to them on a constant basis.
Incubi are trained in the use of many different weapons unique to their warrior sect. This includes Klaives which are big ass power swords, demi-klaives which can be wielded either separately to increase the amount of strikes the user can make or clasped together to form a much larger blade, Bloodstones which are forged from the broken soulstone of an Eldar Exarch that can boil the enemy's blood with a pulse of energy and the aptly named Punisher, a two-handed power weapon resembling a halberd, manufactured in such a way as to assist the wielder when swinging, effectively increasing the strength of their attacks.
Another aspect of Incubi equipment that is fairly unique is their use of power armour like the Incubus Warsuit. This warsuit is used only by Incubi and not even Archons have access to this kind of armoury. The warsuit is as tough as power armour and so perfectly designed it barely inhibits dexterity at all. This means that the Incubi are one of the few Dark Eldar troops that does not fold like wet tissue paper in the midst of battle.
Dark Father is the leader of the Incubi and it is believed that Arhra, founder of the Eldar Aspect of the Striking Scorpions was the original Dark Father. However this is still unproven.
The argument for Arhra being the founder of the Incubi is based primarily on the fact that Eldar refer to Arhra specifically as "The Fallen Phoenix", and refer to Incubi as "Fallen Warriors", stating that their Dark Father had, "Turned from the light into the shadows". Although suggesting that to an Incubi that their leader is a closet Phoenix Lord is the quickest way of getting shanked for Heresy while telling this to a Striking Scorpion is the quickest way of having your anus thoroughly eviscerated.
Piece of useless trivia
If you're wondering why the fuck "klaives" look nothing like glaives despite the names sounding similar, here is a possible explanation. "Klaive" is probably a pun on the verb "to cleave" and the Irish word claíomh (click here if you're not comfortable with Irish pronunciation), which simply means "sword". Yep, sometimes GW can do things right.
|Forces of the Dark Eldar|
|Command:|| Archons - Haemonculi - Kabalite Trueborn |
Lhamaeans - Medusae - Sslyth - Succubi
|Troops:|| Beastmasters - Commorragh Slaves - Grotesques |
Hellions - Incubi - Kabalite Warriors - Mandrakes
Scourges - Wracks - Wyches
|Beasts:||Clawed Fiends - Khymerae - Razorwing Flocks - Ur-Ghuls|
|Pain Engines:||Cronos Parasite Engines - Talos Pain Engines|
|Vehicles:|| Raiders - Raven Fighters - Razorwing Jetfighters |
Reapers - Reaver Jetbikes - Venoms
|Super Heavies:||Ravagers - Tantali - Voidraven Bombers|