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Psions are a race of psychically powered-beings who were conquered and enslaved by the Cabal in the hopes of weaponizing their abilities. They now primarily serve as engineers, pilots and fire support within the Cabal military.
Ancient Psions practiced a form of ancestor worship, communing with the divine spirits of the dead through a Y-goblet that "cupped their spirits" and poured out their souls into new Psions. Worship involved daily rituals in which the Y-goblet was filled with offerings for ancestors, such as water to wash out their eyes, salt to roughen their skin,  or linen to bind their wounds. Other practices included physically drawing the Y-goblet on a nearby surface. Adherents believed that every other person, or at least Psions, had a spark of the divine within them, physically evident in their Y-shaped pupils. 
In prehistory, long before the Psion species joined the Cabal, a group of exceptionally powerful Psions known as the God-Thoughts dominated the species with their psychic abilities. They destroyed the Y-goblet faith for seeing divinity in every common person. Its suppression was so brutal that while the faith survived to the present, its practitioners still feared discovery and worshiped only in secret.
The Psions were assimilated into the Cabal empire either before or during Emperor Calus's reign. They were largely enslaved under indenture, but some were allowed to remain free.
The legendary, clairvoyant OXA Machine has been built, lost, and rebuilt many times in Psion history, passing down from civilization to civilization over the ages.  Its most recent iteration was destroyed by the Cabal, but rebuilt centuries later on Brand by Freeborn Otzot, a particularly brilliant Psion. When Umun'arath moved to destroy this newest version of the machine, Emperor Calus stopped her in recognition of Otzot's genius, and welcomed the freeborn Psion into his court as his Imperial Dreamer.
Late into Calus's reign, he attempted to grant freedom to all indentured Psions, but was overthrown before this could happen. Ironically, Otzot was one of the conspirators against him.
Psions have bald, veined heads, with a single eye surrounded by black trident-shaped creases. These eyes can be either blue or orange, and have distinctive Y-shaped pupils. Their eyes turn opaque grey once they die, and the Y disappears. Their faces have a series of holes above their mouths, possibly functioning similar to spiracles for breathing. Psions serving in the Red Legion have the tops of their heads exposed, even in harsh environments such as Mars, Io, and Nessus without any visible damage. This is likely done to enable them to utilise their psionic abilities more freely, though also implies that their skin is incredibly tough despite its fragile appearance. Psions have five fingers on each hand, though often their armor groups their middle and ring fingers into one. They are significantly smaller than their Cabal superiors on average. However, Kargen, the Technocrat, the Flayer Sisters, and Inotam, Oblivion's Triune are notable for towering over the Cabal under their command..
Psions are skilled marksmen, as they can use their telekinetic abilities to slow their own breathing and steady their aim.  It is very common to see Psions providing long-range fire support for other Cabal units. They can use telepathy to steal secrets from the minds of others . Psions have been described as providing post-op analysis and other intelligence-work for Cabal forces in Sol, and have observed the phenomenon of Darkness Zones (areas in which the ability of Guardians to reanimate is suppressed).  The standard Psions in most legions have psychokinetic blasts that are Arc-based, and which disorient the victims; however, Psions in the Red Legion and Loyalists have Void-based Blasts and attacks. Psions can use their powers to communicate with machines, and even create extra-dimensional portals. They even managed to spy on Crucible matches such as at Firebase Thuria, which oddly enough, bemused them at the Guardians complaining.
Psions seem to have a deep reverence for the lives of those around them, as their clairvoyance allows them to sense them in intense and mysterious ways. They feel the imprints of those around them, noting the powerful gleaming aura of Calus to be so blinding that they cannot see past it. They are unnerved by the Hive, because they appear to have empty minds besides their hate and need to survive. It is likely that Psions are naturally very social, as they have some ability to communicate with each other telepathically and will even combine their thoughts together in concerts in times of stress or necessity. This telepathy may not be wholly consensual or their higher level thoughts are broadcast to some degree. Psions are able to share thoughts to members of selective groups referred to as "metaconcerts," although Calus appears to have been able to take part in them as well. They are also capable of a permanent form of metaconcert called "joining," though this process is only known through "ancient texts of the mind" and the sole example of it in recent history is the fusion of three Psion Flayer sisters into Inotam, Oblivion's Triune.
Within the Cabal Empire, Psions are second-class citizens at best and slaves at worst. They serve the Cabal as laborers, engineers, and mechanics. Psions have worked as pilots as well in their time of service. Their integral part in the Cabal military is seen through the extent at which they rely on the Psions. Maintenance passages in most of their ships and structures are often too small for Cabal to move through comfortably, and Interceptors are designed for use by Psions exclusively. Particularly talented Psions are trained to become Psion Flayers, masters of their incredible power and intellect. The full extent of their abilities is unknown, but they are thought to have been able to alter the orbit of Phobos and possibly break entire worlds.
Certain Psions are not born into slavery and are regarded with the title of 'Freeborn'. They are exceptionally rare in Cabal society and are of vastly superior social standing to others of their race, potentially being considered equal to other Cabal. or perhaps before, as there have been multiple instances of Psions leading significant detachments of Cabal.
Psions will be able to send fourth a damaging wave of psionic energy that travels across the ground, as well as a point-blank psionic attack at melee range. These attacks deal Arc (or electrical) damage, signifying their power over mind and (potentially) machine. Certain Psions are known to channel Void and Solar power, though this is restricted to Flayers observed in the Prison of Elders. Psions become much more dangerous during Nightfall Strikes, as they acquire a Void shield.
A sect of Psions belonging to the Red Legion utilize new Void-based abilities as well as Cabal Headhunters. A minority continue to use Slug Rifles, and a few elites use Cabal Slug Shotguns. These Psions have an upgraded version of their old wave attack, now referred to as a "rupture ability," which explodes and launches enemies into the air. They also have jetpacks, which they can use to maneuver and travel at high speeds. Red Legion Psions have the upper parts of their heads exposed.
The Loyalists have a special version of Psions called Councilors, which have special abilities used throughout the Leviathan raid. They float in mid-air and are surrounded by a shield that blocks all projectiles, but are still vulnerable to melee attacks.
List of appearances