Reacting with the instinctual disgust any human feels when confronted with a Parasite. Magnus reached out with telekinesis to end the abomination. He would not be satisfied merely bursting the creature like an infected pustule, it needed to be wiped out with overwhelming force. The edges of the Obelisk-hab deformed as if gripped by the hand of an invisible giant. Which in a way it was. Magnus ripped the massive spire from the ground. Lifting the three hundred meter tall building into the air and bringing it crashing down. Aiming at one of the entrances of the Plaza like some god-thrown javelin. Even after it struck, Magnus kept up telekinetic pressure. Slamming down on the rubble and closest buildings with a psychic bombardment. Reducing nearly a square kilometer to perfectly flat stone.
The Primarch knew the source of this world's heresy. The nature of what turned Prospero into a planet beyond Imperial Compliance. He had read of many dark and terrible things in his father's library. Of the nightmares that stalked the Warp and fed on those touched by it. Of those Warp Predators, few roused the wrath of Magnus Rubricar like Psychneuein. Ancient hybrid organisms of both the Warp and Material. Taking the form of giant Parasitic Wasps. They laid eggs in the brains of Psykers. Overrunning entire planets in great feeding swarms that would descend on beings with even the slightest psychic talent. Magnus had never fought them before, and what he found on Prospero did not fully match the texts of the Imperial library. Yet the brain-eating parasites were instantly recognizable. Something horrible had happened on this World and Magnus would put an end to it.
The Primarch and his honor guard moved towards the Great Pyramid. The Terminators lagging behind the Archmagi and his twin Equarries. Forming a rearguard as Magnus ascended the Pyramid. It was a grand structure of polished metal and stone. Combining ritual elements and functional architecture. A staircase large enough for even a Primarch to walk cut into the Pyramid. Leading towards a cavity halfway up the structure. The psychic echoes of thousands of minds covered the steps in a spiritual miasma. Each a Psyker of some power bred for an abominable surface and taken to the Pyramids heart. Sparks of lightning rippled around Magnus as he ascended the stairs. He could feel the formidable psychic presence inside the Pyramid. A great tumor of raw power at the heart of an ever-growing Web that stretched across Prospero. To his surprise, the presence offered no resistance to his advance and he wondered if it had even noticed him. Something was wrong with this scenario. On many occasions Magnus had faced down powerful Psychic horrors, yet nothing quite like this. The thing in the pyramid felt… unfocused and unresponsive. A great mass of psychic power lacking a true ego. Power and control without a guiding mind. Prospero found itself shackled to a blind-idiot god, barely aware of its surroundings and content with a sated Id.
It did not make sense, such an entity required direction and intelligence to survive and thrive as it had. The answer soon entered the Primarchs awareness as he neared the Pyramids maw. Nestled within and behind the central psychic nexus was a second mind. A human Psyker, bound up in the Psychneuein infestation's heart. The mind was old and powerful by baseline human standards. Connected to the greater power but not shackled to it like the rest of the population. This was the true mind behind the heresy of Prospero. It would die and its leviathan instrument of psychic dominance with it.
Reaching the top of the stairs, Magnus Rubricar entered the belly of the beast. Beautiful mosaics and carvings lined the passage into the Pyramid. Generations of artistic talent trying to make a Monsters lair beautiful. It did nothing to hide the all prevailing stink of mind-death. The slow and deliberate consumption of psychic minds by parasitic warp predators left a distinct imprint on the environment. Different from the taint of Chaos, festering contamination instead of the lunatic contagion of the Dark Gods. Magnus pushed past it, letting the flames of his soul burn away at the miasma. A brief telepathic message ordered his honor guard to defend the Pyramids entrance. They would be little help against what he was about to face.
The Primarch, flanked by the twin Magi, entered into the abomination's nest. A huge hollow space within the Pyramid stretched out before them. Magnus could only guess at the true size of the chamber as the majority of it was filled. A massive insectoid horror adhered to the roof and walls of the chamber. The form of a Wasp distorted into a twitching mass of warp-soaked tissue. Here at the heart of the psychic web the strings of influence were so concentrated they became visible to the naked eye. Bundles of fiber similar to Arachnid silk and Neuron dendrites covered the monster. Streaming across the chamber and into the Immaterium, then across Prospero. Magnus felt the panicked thoughts and base desires of the entire Amonite commune radiate off the threads. Concentrated psychic filaments leaking a steady stream of primitive spirit discharge into the chamber. The murk of a people dying at his Legions hands only added to the horror as Magnus traced the distended body of the creature.
Long reproductive organs that mingled common biology and warp-born nightmares dangled down to the chamber floor. A dozen of the lesser-nexus Abhumans, of the type Magnus had killed with its own Obelisk, was connected to the stringy ropes of flesh. These abhumans were younger, barely on the cusp of adulthood with bodies not yet fully atrophied. Each had one of the monster's organs inserted into a facial orifice. Magnus did not need to focus with his transhuman senses to know what flowed through the invasive tubes. Psychneuein eggs pumped into a perfect nest. This made little sense. Psychneuein grubs devoured their host in days. How were these Abhumans living, and even functioning with this infestation? The skies of Prospero should be black with Psychneuein wings and its population devoured years ago. Was this some part of the Warp-Parasites life cycle unrecorded by Imperial records? No, this was an unnatural perversion of an already unnatural process. The creature dangling from the ceiling was the infestation's Queen. There was no doubt of that, but it had been altered in some fashion.
A twitch of movement from the horror before him pulled the Primarch back to present. With a mental command, his Staff's meteorite head glowed with crimson light. Illuminating the source of the movement. A human male, withered by time and pain, disentangled himself from the Psychneuein Queens tendrils. He lacked the mutations ubiquitous to Propero, and he reminded Magnus of some of the scholars in his father's employ. With unsteady feet, the man approached Magnus and tried to speak. He doubted the man had used his vocal cords in years. After a few tries, the man spoke in heavily accented Gothic. "I am Amon of Tizca. Who are you Giant? Why have you come to burn my world?"
Magnus looked down on the relic of a man. The guiding intelligence of the Commune that bore his name. A momentary flicker of pity and empathy crossed the Primarch's mind. He did not know the source of the intrusive feelings and quickly locked them away. Peering down at the mortal man who had somehow broken a Psychneuein Queen, Magnus spoke. "I am the Primarch Magnus, fifteenth son of the Emperor of Mankind. I bring destruction not out of malice or hate. I do it because it must be done."
Gesturing up to the Queen, Magnus continued: "This world and its people are an abomination. Heresy in the highest order and not something that can exist in Mankind's galaxy"
Amon let out a breathy wheeze that might have been a scoff. "Heresy? You cannot be serious? You tear down all I have created and slaughter my people because of Dogma"
Magnus looked down at the warped little human, he was surprised this Amon had not reacted to his presence. Perhaps years in the company of the Psychneuein Queen had inured him to the influence a being such as a Primarch could have. In any other case, Magnus would have blasted the Heretic leader from the universe and be done with it. Yet a nagging feeling in his soul sought to justify himself to Amon. "Heresy is a very old and loaded word. At its core, it means something that deviates from the chosen creed. Something that threatens the legitimacy and purpose of a broader idea. My father favors such archaic terms, believing them to hold a certain power later more nuanced words lack. I can understand his reasoning and judge you by his truth as a Heretic. A heretic towards the only creed that truly matters and why the Imperium exists. The survival of mankind is paramount and your actions are a heresy against our cause of survival."
Magnus did not expect the reaction he got. Amon focused on him with a vicious intensity and snarled at the Primarch through age-worn teeth. "Survival? You judge me and exterminate my people in the name of survival? You are an utter fool. Why do you think I took such drastic actions to protect Prospero? Do you think I wanted this? The Psychneuein grew more numerous with each passing year and the Aether grows ever more turbulent. We would have been wiped out, either by the Psychneuein or another Spiritual Predator. I did what needed to be done for us to Survive!"
Amon gestured to the chamber around him and up towards the warp-xeno nightmare. "I saw an opportunity, the Queen was weak just after molting. Nearly two dozen of our greatest mind-walkers died but we broke the Queen. Crippling her mind and finding ways to placate her instincts while also surviving. Prospero's children host her children. Her influence keeps them from fully developing and protects those implanted from the Sea of Souls. We turned a Parasite into a symbiote, yes sometimes the process fails, but we survive at any cost. Surely you can recognize that?"
The shriveled Psykers anger echoed throughout the room and his captive Queen twitched, feedback from whatever telepathic shackles wormed into its mind. Amon continued his rant: "Look at you Magnus, a product of flesh-crafting and soul-stitching. Forged to fight wars you claim are for mankind's survival. You are living proof that in times of darkness we must take extraordinary measures to live another day. You judge me with the certainty of a hypocrite."
With an apologetic flick of his fingers, Magnus gripped Amon with a telekinetic vice and lifted him into the air. The Primarch easily punched through the Heretics defenses and dominated him utterly. Magnus moved the struggling psyker so he could look the man directly in the eye. With a deep breath, Magnus Rubicar opened up his third eye. An occult sigil in the form of a glowing eye ignited on the Primarchs forehead. A manifestation of the Primarch's power and connection to the Warp. Product of years of intense focus and training. The Eye of Magnus acted like a Navigator's own third eye, except crafted entirely from Psychic energy, and far far more capable.