Psykers
Psykers (Homo sapiens veneficus) are humans born with extrasensory perception and the ability to call upon the the power of the Warp. At face value their powers are miraculous; an unrestrained Psyker can reshape reality at will. But they are one of the greatest threats to humanity. Their deep connection to the Warp makes them even more vulnerable to the corrupting influence of the dark powers dwelling within it. Each Psyker is a beacon drawing towards them Warp-predators who seek to use them as a conduit to enter reality and prey upon mortal souls.
This mutation is not unique to mankind; many Xenos species possess similar extrasensory abilities, leading some to surmise is it a natural part of evolution rather than the touch of the Warp. Be that as it may, psykers remain a major threat to themselves and those around them, and the Imperium treats them as such.
The question of what to do with Psykers has plagued the Imperium since its foundation, and humankind since long before- over the course of history Psykers have been hunted and burned, used as tools of war, even worshipped as god-kings - but normal humans have always feared them. In the long night, the Age of Strife, more and more Psykers began to awaken, and their awakenings brought cataclysmic events to their worlds.
When the Imperium rose, Psykers were a persecuted species. To the Imperium of the 41st Millennium they are one of its greatest threats and greatest assets; whole fleets of vessels travel the Galaxy filling their holds with Psykers to bring back to Holy Terra. The Imperium knows that every Psyker it finds can be turned into a potent weapon against its foes, but that every one left unattended is a potential gateway for far greater threats.
The Black Ships and the Assignment
Every Imperial citizen lives in fear of when the Black Ships come to their world. With them they bring legions of Psyker Hunters and the strange Psi-Hounds they bring with them. They come not only to collect the tithe of Psykers from the holding cells of Imperial authorities but to hunt those latent psykers who have gone unnoticed, scouring the world of any potential threats.
Once the bellies of these ships are full, only then does their shadow leave the world they are visiting, and they begin their slow, ponderous, route back to the final destination of their occupants, Terra, the Imperial Throneworld.
Black Ships arrive at Terra daily disgorging the Psykers they have collected to be shuttled down to the Imperial Palace where they will begin the long walk to their destination. Scores of Psykers walk through the great arches of the City of Sight, the headquarters of the Adeptus Astra Telepathica, which has monitored and trained Psykers since the first days of the Imperium. The Adeptus assesses each psyker that enters the City, in a ritual known only as the Assignment. Barely a handful of the many thousands of psykers that enter daily pass; the majority are determined to be too weak, or too unstable to be of value, and sent on to a second destination.
The Imperium has names for those that emerge from the Assignment. Those that are selected initially are called Primaris Psykers. These individuals will be trained in a variety of roles, from combat psykers to telepathic interrogators, and taught to use their powers in a stable fashion.
It falls to the Adeptus Astra Telepathica to teach these individuals how to handle their powers, to police them and ensure they don’t fall from the light. For the rest of their lives these individuals will never be free from constant scrutiny. There are a small number who slip beyond the reach of the Adeptus Astra Telepathica, such as those Psykers who join the Inquisition; for they answer to the authority of their Inquisitors, and the Throne, alone.
Astropaths and the Soul Binding
Of the thousands that fail the Assignment, they continue their journey on from the City of Sight to the Forbidden Fortress. It is here that the Adeptus Astra Telepathica’s sister-organisation the Adeptus Astronomica, the Priesthood that tends to the astral beacon known as the Astronomicon which all Imperial vessels use for navigation within the Warp, awaits them. Of the several thousand Psykers that enter the Forbidden Fortress each day, only a few emerge, nobody knows exactly what happens to those who don’t return from the Fortress.
Those Psykers that emerge later from the Forbidden Fortress are called Astropaths. These form the Imperial interstellar communications network, telepathically receiving and sending encrypted messages across vast stellar distances which no technological device could bridge. What they endure within the Fortress changes them forever.
Within the Forbidden Fortress these individuals are subjected to a ritual known as the Soul Binding. These individuals are deliberately exposed to the blinding golden light and raw psychic majesty that is the God Emperor's psychic essence. Most die in the process, but a handful survive the experience; these individuals have their psychic power strengthened by a form of psychic bond with the Emperor, but the experience is horrific for any individual that participates.
The side effects of the soul binding are myriad; all lose their natural sight - some even have their eyeballs burnt from their sockets, and will in turn have to learn to see with their psychic senses or undergo expensive cybernetic augmentation. There are many other scars that can occur from the process, from displaying stigmata from the wounds the Emperor suffered in His final battle to long-term physical impairment.
Psykers within Imperial Society
Imperial Psykers are chattel. Any human psyker is considered legal property of the Imperium; they do not possess the rights of an Imperial citizen. Murder of a Psyker is not considered murder at all, but rather destruction of Imperial property. A Psyker needs permission for the most basic life decisions, their food and accommodation is provided by the Imperium, the right to have children, or even enter into a relationship is in the hands of their Imperial Masters, the Adeptus Astra Telepathica.
Psykers tend to be housed together for as much mutual protection as segregation. Imperial citizens are raised to abhor Witches, and often tend to blame unexplained misfortunes on the Warp;, known Psykers are often targeted for this reason.
The majority of Psykers spend their lives in service to the various branches of the Imperium; an Astropath may be seconded to a Naval Vessel to act as a vital line of communication, a Telekinetic might be assigned to an Imperial Guard unit as a Battle Psyker, using their powers to devastate the enemy, or a Telepath might be assigned to the Adeptus Arbites as a Psi-Judge.
Some Psykers, however, enjoy the patronage of individuals wealthy enough to pay the extortionate fees charged by the Adeptus Astra Telepathica to buy a Psyker’s contract. It is rare for a Psyker to be given such an opportunity, and often the individuals capable of this extravagance can give them a lifestyle vastly superior to that which they normally enjoy.
Branding
While Imperial propaganda likes to show Psykers cowed and visibly branded (usually on the forehead), the fact is that it's exactly that: propaganda. Such clear branding would make many psykers useless for espionage/undercover and generally sensitive missions for their Inquisitorial masters. Many psykers come out of the City of Sight with obvious brands, these are usually the brands they are left with for life.
However an Inquisitor could petition the Adeptus Astra Telepathica to have an Acolyte re-branded for their own purposes, for example to make them valuable for undercover work. Few other factions (other than the Adeptus itself) have the sway to arrange a rebranding There is a series of possible types of brand:
OBVIOUS - these are permanently visible or incredibly hard to conceal (forehead, cheek, etc.) Less trusted or newer members usually have them.
EASY TO HIDE & EASY TO SHOW - most active and trusted Acolyte Psykers will have brands that aren't easily spotted but can quickly attest their licensed state without much effort (between the collarbones, inside of the arm, upper arm, ankle, basically any bit of one's body that can be covered with clothing but exposed without requiring loss of clothes).
CONCEALED - Deep undercover agents might have their brands so well hidden that they are not visible without an examiner knowing exactly where they are - or if the psyker shows them (some examples include on the roof of the mouth, covered by a flap of synthskin, branded on a shaved head, then letting the hair regrow, etc). Extreme cases (like a brand performed during surgery on the INSIDE of the Psyker's skin) can become a problem (a bloody one, too) if the psyker needs to physically show it.
NON CORPORIS - These are brands not placed on the body of a psyker. They're rare, but not unheard of. There are many reasons for this, including injury, loss of the part of the body that had the brand, or a requirement for deep undercover work. Usually, Non Corporis brands come with a certificate that reads just like an official brand identifying the Psyker as sanctioned. The holder of a Non Corporis brand who misplaces their paperwork is likely to attract serious and potentially lethal consequences, without a high-ranking sponsor’s intervention.
All brands have one thing in common: a specific minting technique that identifies them as being authentically Imperial. Any individual with Hereticus lore can tell true from fake, but it is believed that that is not the only way to determine a brand’s veracity. The branding process, it is said, contains unknown elements that allow members of the Departamento Investigates/the League of Black Ships (and their Psi-Hounds) to be able to sense a brand’s authenticity even without seeing it, and even (rumour has it) hunt down specific psykers by the design of their brand.
Processing Unsanctioned Psykers
Psykers, for all that the Imperium treats them as second-class citizens, are a valuable commodity. Occasionally newly emerged Psykers are missed by the Black Ships and escape detection to remain in a population.
It is a breach of Imperial law to hide or fail to report an unsanctioned Psyker or for a Psyker to not present themselves to Imperial Authorities - the life of the unsanctioned psyker is not a happy one, for they will always live in fear of being discovered and reported, even by those closest to them. The following is an excerpt from official Arbites guidance on encountering an Unsanctioned Psyker:
So you have encountered an Unsanctioned Psyker (UP). While this individual walks in defiance of Imperial Law, you are dealing with an individual who may be a potential asset to the Adeptus Astra Telepathica. However no asset is worth imperilling the Imperium, so consider the following questions upon approach of the suspect;
1. Is the UP wilfully endangering you or other Imperial lives? IF YES, terminate immediately. IF NO, keep reading.
2. Is the UP displaying signs of taint/vomiting ectoplasm/rotating its head more than 110 degrees left or right? IF YES, terminate immediately. IF NO, keep reading.
3. Is the UP unwillingly endangering you or other Imperial lives? IF YES, can you affect capture of it without endangering yourself and others more than would be considered reasonable? If you can, do so. If you cannot, see 1. IF NO, detain the UP as effectively as possible (sedation is an effective method) and summon the Departamento Investigates of the Adeptus Astra Telepathica.
New Psykers are a valuable commodity to the Imperium and the Adeptus Astra Telepathica dislikes anyone destroying potential future assets.