Abyssal Cults

Abyssal Cults are a threat that is believed to be long gone by majority of Mankind. Something out of the dark days of the fall of Solar Commonwealth, a nightmarish myth of hyperspace-tainted madmen gleefully committing attrocities that would made the likes of Hitler or Delacroix vomit. A myth defeated and scattered during the Slave War, when both the insurgents and the Solar Commonwealth cooperate to destroy them before returning to their interrupted war.
This is, unfortunately, a lie. Abyssal cults, though no longer a monolith, are still active. They were forced to retreat to the Discord, and they no longer possess the manpower neccessary for staging planetary raids of their own. However they persevere. And seem to be slowly regaining their power, by offering their support to pirate and transhuman warbands roaming the edge of civilization. Which makes them one of the most common threats that the Explorer's Guild has to face.

Structure

Most of the major abyssal cults are internally divided according to a strict hierarchy. In every warband there is (almost) always one person with absolute power as the head (termed Heresiarch by the Res Publica Christiana, a name that spread so far that even the cultists themselves began using it), then a number of elites/officers/'priests', and finally the footsoldiers. The size of the warband - and the size of all three stratas of the cult - heavily varies.
However, there are also abyssal cults that notably diverge from this pattern, for example the minor abyssal cult called Apostles of Freedom who tend to lack the heresiarch, and instead is governed (in a weird way) via direct democracy. This makes describing the cult structure rather troublesome. In the end every abyssal cult is a separate case, sometimes much different and sometimes quite similar. One certain thing is that every cult has at least one supreme leader, typically residing in Discord. The largest abyssal cults have their leaders (sometimes - and unofficially - dubbed High Heresiarchs) be a part of the Council of Woes.

History

The first abyssal cult was born among the flag officers of the Reserve Fleet of the Solar Commonwealth during the years preceding the War of Purity. With its origins shrouded in mystery, nobody is sure how exactly did it began. What is sure is that the cult spread, both among the flag officers and lower ranks, finally culminating in year 2309 with entire Reserve Fleet going renegade. While some of its ships became pirates and other vagabonds, the core of the cult formed the Silent Sorrow abyssal cult. It remained the only abyssal cult until it began collapsing in the aftermath of the disastrous defeat at the hands of the Solar Federation in the battle of Civitas-IV.
This lead to Silent Sorrow itself declining immensely, but also to a creation of a number of new cults, such as the Unblemished, the Burning Court, and the Murder of Crows - each of them equally even if differently unhinged than the Silent Sorrow. Today it is unknown how many abyssal cults are there, but it is believed that there are around twelve major ones, and an unknown number of minor cults (most of them fleeting and rarely controlling more than a handful of ships). With the entire Human Space being utterly hostile to the cults, they reside in the Discord - the only place where crazies like that can live without getting torched.

Demography and Population

It is believed thata abyssal cultists are 'born' from people exposed to Hyperspace too much, whose Hyperspace Schizophrenia somehow molds their mind into a stable (even if utterly unhinged and insane from normal human point of view) form, instead of keeping it as a disfigured mess. It is unknown how exactly this happens exactly.
It can happen at random to people under a too heavy exposure to the Hyperspace, however this is extremely rare and tends to end with such a rare cases typically killed quickly. Because of that, it is believed that the cults have some sort of a way to do that to captives (at least some of them) in a way that offers a high percentage of success. How exactly is it done, nobody knows. For while the abyssal cults are utterly unhinged, their understanding of Hyperspace seems to be a step before even the most advanced countries.

Military

Every abyssal cult fields at least a single raiding fleet (from few lighter ships to entire squadrons of battlecruisers or even some pocket battleships and fast battleships, but it's extremely rare) that launches raids against trade routes and outlying settlements of the Human Space (or the aliens that border it). It's their main source of slaves, sacrifices and various goods that they can sell to other powers of Discord in order to maintain their power base.
Pretty much every cultist is a combatant, typically around the level of regular armies of Mankind - underestimating them because of their insanity and often 'disheveled' equipment is an easy way to get killed. They are also known to field an unheard of number of anomalists, sometimes fielding entire companies of them. Most of their officers and almost all heresiarchs are powerful anomalists too, which only heightens the threat that they are.
If all of that wasn't enough, they are also known to amass astounding ammount of archeotech wargear, including darktech things that are better left buried and forgotten.

Cosmological Views

It is hard to sum up the cosmology of the abyssal cults, mostly because the fact that in spite of their many similarities, the 'theology' of every cult is slightly bit diferent. What is fairly certain is that they all seem to believe that Abyss is not a location, but instead an entity (or a number of them) that can be considered 'gods' of the abyssal religion. The cultist approach to them is one of equal worship... and terror. Abyssals believe that it is only a matter of time before those entities devour Reality, for it is an anathema to them. Those entities predate time, and will exist once it's gone.
Many abyssal cults are recently undergoing internal strife due to spread of the theory about the Archenemy. They aren't sure if that's one more representation of the Great Abyssal God/s or something else entirely. The theory that the Archenemy is a chosen weapon of their gods seems to be steadily gaining the majority.

Tenets of Faith

The only tenet that all the abyssal cults share is to make the Galaxy burn in the name of their god/gods. Murder, rape, torture and genocide are almost holy acts, while wrath, lust, envy, pride and general self-indulgence are virtues. It's as if entire value system of a normal person was 'flipped' during the process of their minds adapting to the Hyperspace Disease and then stabilized in that form. They seek nothing but utter ruin of everything that exists, in order to pave the way for their masters to devour the ruins of Reality.
If there was ever a religion that was also a mental disorder, it was certainly this one.

Worship

There is only one way in which the abyssal cults seem to worship their eldritch gods - sacrifice. Of sapient species, preferably humans but it's not unheard for insectoids or even berserks to be caught and sacrificed by the abyssal cults. In fact everything sufficiently intelligent will pass. Sacrifice methods vary between abyssal cults, what remains unchanged is that only part of the captives will be sacrificed. It is believed that the cults know who can be 'converted' to their cause via directed hyperspace exposure, and prefer to recruit such captives. A fraction of captives will be also sold in Discord for money. The rest? Tough luck.

Sects

There is about a dozen of major abyssal cults - and an undetermined number of lesser ones that seem to come and go. Each of them has its own rituals, deities, aesthethics and tactics, essentially forcing to describe all of them separately. Here only the most notable ones will be summed.
Silent Sorrow - The oldest abyssal cult in history, that became well-known after their almost a century long rampage through the Human Space that lasted from year 2309 (when the Reserve Fleet went renegade, a part of it forming the Silent Sorrow cult) to year 2408, when forces of the Solar Navy succeeded in trapping and destroying seven battleships and twenty-two cruisers - essentially 2/3 of the cult - during the battle of Civitas-IV.
Silent Sorrow follows a highly nonsensical doctrine that seem to venerate cannibalism as, in a way, vampirism (for them it is a way of 'devouring' one's 'lifeforce'), combined with a perpetual mourning after the world that is soon going to pass. They devour lifes to save whatever can be saved from this doomed world - after all why would all the lives go to waste? The result is perpetually sorrowful and melancholic cannibals. That also seem to surgically remove their vocal cords, so that only their 'gods' can hear them.
It's the oldest and most well-known cult,it was destroyed several times. Which means that it was announced destroyed after suffering heavy casualties at least several times, but managed to recuperate each time. After the Solar Federation in battle of Civitas-IV, it was also devastated by the two other main antagonists of the Galaxy (Truthseekers Corporation during the War of the Outlaws and the Fourth Reich during the failed raid of Nietsche-III), and also by the US Navy (late Unification Wars) and, recently, by the warhost of princess Rose Dunecki. It seems to eventually return stronger from any such event, but for now it's in a state of disarray.
Burning Court - Burning Court is a splinter group of the Silent Sorrow that emerged in the aftermath of the battle of Civitas-IV and remains one of the most powerful abyssal cults in existence. Unlike Silent Sorrow with its propensity for larger fleet maneuvers, Burning Court operation follow a more standard abyssal cult pattern. It prefers to deploy small strike forces that are spread throughout the Galaxy. It also lends their ships (or entire companies of stormtroopers) to other Discord powers.
Burning Court is an organization of fanatic purifiers that see the Galaxy as essentially doomed. They see themselves as a group tasked with mercy-killing of the universe. They seek annihilation of all life, with not even traces of it remaining. All who doesn't offer prospects for recruitment are ceremonially burned (typically - alive, though finding an explanation for that in the Court's jungle of a theology might be troublesome), their ashes then dissolved in acid to ensure that nothing is left.
Burning Court is somewhat a subversion among the abyssal cults, as they (on multiple occasions) engaged other cults in battles, often interrupting their raids against 'civilized targets'. Unfortunately, all of the 'liberated' prisoners were either inducted into the cult or burned alive, making them... a bit less of a heroes (though, admittedly, death by being burned is much faster and much less painful than what some of the others cults excel in).
Unblemished - Another splinter group of the Silent Sorrow that emerged in the aftermath of the battle of Civitas-IV. Like the Burning Court, it remains one of the most powerful abyssal cults in existence. It follows a rather standard pattern of operations, lending troops and ships to various pirate warlords, hunting ships through the edge of the civilization, and generally being less than pleasant to everyone around them.
Unblemished believe in absolute negation of things that make people unique. Unblemished undergo massive surgeries to render them 'perfect' - unfortunately in their case the 'perfection' means surgical (and biochemical) elimination of not only libido but also all sex-related bodily differences, essentially making all Unblemished sexless. They also use extensive mentalsculpting (and straight brainwashing) to eradicate all sense of individuality, essentially changing themselves into armies of mercilless humanoid automatons that unconditionally obey orders of their superiors (that, notably, aren't that much more individualistic than regular Unblemished).
Unblemished are among the more disturbing cults. Their hatred for individuality is well known. When attacking a ship or a settlement they will target the wealthy, the religious, the freethinkers (like artists or writers) and even people with more notable masculinity/femininity with extreme ferocity, which was on several occasions exploited by the defenders preparing to battle against the Unblemished.
Murder of Crows - Murder of Crows is third (and last) splinter group of the Silent Sorrow cult, created after the disaster of the battle of Civitas-IV. Like the Burning Court and the Unblemished, it remains one of the most powerful abyssal cults in existence. It follows an unusual operation pattern, as not only it seems to excel in rapid planetary assaults, it also tends to avoid cooperating with other groups of Discord.
It's hard to say what exactly does the Murder of Crows believes in, as they are one of the most secretive abyssal cults in existence. What is known is that they seem to like various feather accessories, excel in voidcraft engagements and often use great number of geneengineered crow-like creatures armed with paralytic poison (and limited cybernetic enhancements) in their planetary assaults. They are trained to keep low attitude, and swarm enemy positions and cities en masse, paralysing hundreds of people that can be then kidnapped by the cult (plus typical pillage of everything that's valuable).
Murder of Crows is also unique in the fact that it seem to go for quality instead of quantity in their sacrifices. They rarely sacrifice more than 2% of captives (though it is unknown how they choose them), and after picking those viable for induction into their ranks they sell the rest as menial slaves in the Discord.
Church of the Abyssal God - A relatively recent newcomer to the party, Church of the Abyssal God has managed to rapidly grow in size, soon becoming a power to be reckoned with (unfortunately to the world). It follows a relatively standard operational pattern, but it also seems to be interested in infiltrating various Res Publica Christiana and Conservative Bloc nations. They tend to 'masquerade' as various missionary groups and lesser known religious orders, taking advantage of local hospitality to steal goods and kidnap people before suddenly disappearing.
The Church of the Abyssal God believes that Abyss is in fact the bibilical God, who was grossly misunderstood during the past 2,7 millenia. Their God is roughly based on the Old Testament one, but not only they got rid of all redeeming (and in fact good) qualities, they also amplified everything else up to eleven and added the things that would fit the most stereotypical antitheist depicture of Middle Ages (whipping, self-mutilations, burning the witches), for no apparent reason. They even use similar clothes to the Roman Catholic clergy. It is no surprise that the Catholic Church considers eradication of the Church of the Abyssal God as their priority, especially as the Church is actually believing that the Archenemy is the long awaited Messiah.
Church is rapidly growing in strength, making their presence increasingly known. It is believed that it's only the matter of time before the Church begins launching planetary invasions, at least on worlds of secondary value. It is believed that at least partially this growth in power is caused by open missionary work throughout the Discordian society.