Random idea that came to me while working on something else.
An SI as Konrad Curze from Warhammer 40k. The SI's introduction into Warhammer is smashing into the core of a planet that makes Gotham at its worst look like Eden. Compounding the issue, the SI is constantly plagued by prophetic visions of possible futures and constantly has dark whispers plague his mind as he is an extraordinarily powerful psyker and he is subconsciously, constantly, reading the minds of the nearly fifty billion people populating Nostromo.
Given that this is a population were more than 49 of the 50 billion will commit cannibalism at some point in their life as a means of staving off starvation and murder, rape, theft, assault, and all manner of other crimes are so common that virtually every individual on the planet will see them all in person at least once a week; it should be pretty obvious why this is a hellish existence for Curze.
Eventually the SI realizes where he is & that he is a Primarch and begins attempting to master his psyker powers. After getting an at least semi decent handle on them he proceeds to begin truly improving Nostromo.
He uses his psyker powers to locate those relative handful of individuals who have, despite every pressure against it, remained un-corrupted and gathers them to himself. He trains these individuals as assassins, calling them the Night Lords, and with their assistance begins a purge of those individuals who most negatively impact Nostromo.
Between his psyker gifts and Primarch abilities it takes him less than ten years to have the place noticeably improved.
Unlike the canon Curze who simply killed every criminal, SI!Curze focused largely on those with power and worked his way down. Corrupt police, officials, judges, etc. where his primary targets.
Nostomo's wealth was a side effect of extracting the mineral wealth of the world (mostly the adamantium) and exporting it to a Mechanicum forge world a system over (the Mechanicum used Tau like drives to avoid the warp storms). SI!Curze renegotiates what the Forge World pays in exchange for those raw materials. Instead of luxury goods he sells Nostromo's wealth for the infrastructure needed to actually improve things; the tech needed to produce enough food, provide clean water, healthcare, etc.
After the Emperor recovers him, his Legion becomes the most precise of all the Legions. Much like the Alpha Legion they focus on stealth, but it is stealth in support of a cleansing fire that will burn away corruption from worlds. Curze selects psykers personally from among the stock gathered by the Emperor and trains his Librarians personally, but unlike Magnus he rejects utterly and completely any dealings with warp entities or Sorcerery.
In truth, Curze is essentially the first Inquisitor and his Legion's role that of the Inquisition.
When he tells the Emperor of his "visions" of Horus betraying him and the Horus Heresy, the Emperor confides in Curze that he is aware of that possible future but that it is a risk that must be taken as on any path besides the current one humanity will be wiped out. Even the "bad" future of the Heresy will ultimately result in a human victory, it will just be unimaginably more costly and take far longer than a future where Horus remains loyal.
Alas the Heresy still happens but with one less traitor and the prep work that SI!Curze has undertaken it is less destructive. SI!Curze sits on the Golden Throne instead of Malcador and when the Emperor is brought before them comatose, he convinces Vulkan to attempt to heal the Emperor instead of Malcador (Vulkan being stronger, being a perpetual, and SI!Curze convincing him that the Imperium needs either the Emperor or Malcador at its helm in the aftermath of the Heresy). This is more effective than Malcador's sacrifice would have been but only somewhat so, and Vulkan is permanently killed.
In the reorganization that follows, SI!Curze is named Grandmaster Assassin and the head of what is effectively the Inquisition. He begins the internal purge of the Imperium to remove the taint of the traitors. Guilliman is named Warmaster after the Lion disappears into his coma and reorganizes the Imperium's warmachine with an eye to ensuring that another Heresy can't occur. Russ, Khan, and Corax lead their Legions on a campaign to actively scour the traitor legions from the galaxy and eventually end up with largely their canon fates. Dorn is charged with fortifying the Imperial Palace, Terra, and Sol to the point of unassailability.
After things have mostly settled down, the Legions are largely reorganized into Chapters. This is not an absolute though, nor is the size of each chapter. The Imperial Fists, for example, are limited to ten thousand battle brothers but these Ten Thousand are oathsworn to never leave Sol and charged eternally with its security. Every member of the ten thousand is a veteran of one of the Iron Fist successor chapters who has had their progenoid glands removed and proven themselves via exemplary service. When there is a vacancy in the Ten Thousand, each of the successor chapters send a veteran of their choice to Sol to potentially fill it and then all of those candidates compete against one another until the best is selected to fill the spot.
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Thoughts? And anyone is free to use this in whole or in part if they want.
