Stygius Sector

Map of the Stygius Sector.

The Stygius Sector used to be part of Imperial space in Segmentum Obscurus and Ultima Segmentum. It is quite known for the fact that it is the location of the motherfucking Mordian Iron Guard, the hardest motherfucking Redshirts you can find outside of Cadia and Catachan. Unfortunately, during the 13th Black Crusade, Failbaddon finally succeeded in his plans on conquering Cadia (Sort of? It was more accurate to state that Abbadon conquered pieces of Cadia) and ended up splitting the Galaxy in two. This giant galactic gaping vagina known as the Great Rift caused a psychic blackout to the northern parts of the Imperium. Mordian and the other systems within the Stygius Sector was plunged in a dark age, now vulnerable from whatever gubbins waiting just around the corner.

Currently, the entire Sector is under the control of the Thousand Sons, with Mordian being the unofficial de facto capital of the Stygius Sector (Although it is technically not an official capital de jure) whilst Sortiarius and Prospero remains the dual capital in the New Kingdom enclave. This means that Magnus' government is unique in that it has three capital locations at once. Of course the Imperium does not recognize the newly acquired territory, instead viewing it as an occupation, meaning that the Stygius Sector is the largest known unrecognized territory in the galaxy. Furthermore, the Scourge Stars would most likely not recognize the Stygius Sector as territory owned by Sortiarius due to Tzeentch's foreign involvement and meddling within the Death Guard's domain. Magnus obviously rejects the lack of Imperium recognition as he views it as a territory that was won fair and square.

Invasion of the Stygius Sector or how Magnus and Tzeentch suddenly put on their Manifest Destiny Hat

After seeing what Morty and friends did in realspace with the creation of the Scourge Stars (Who ironically got inspiration on how Magnymagic got Sortiarius out into realspace with a good Yiff kicking), Tzeentch and friends decided why not do the same? And so they did with the sudden invasion of the Stygius Sector which was now vulnerable from Chaos incursions due to the current astropolitical climate of the galaxy. Magnus (After somehow escaping the labyrinthine psychic rainbow road known as the Webway without a map) also decided that just popping Sortiarius over his old home system of Prospero wasn't secure enough and decided it was in his best interests to exploit the political situation and expand a bit. Although why Magnus and co decided it was a good idea to set up shop from the other side of where Sortiarius is located in the Great Rift is unknown (Possibly to create a distraction to the Imperium so that Sortiarius won't get invaded?).

Anyways, the opening phase of the invasion saw Cult uprisings begin across a score of the Sector's isolated worlds which is further helped with the actions of the Changeling adding further fuel to the Sector's troubles, as the Daemon traveled from world to world, spreading havoc and confusion. However, it was only when the Stygius Sector's worlds were seething with rebellion that the true invasion began, as Tzeentch's Daemons and Chaos Space Marines were unleashed upon the Sector. With the Daemon Primarch Magnus and his Thousand Sons, along with the Lord of Change M'Kachen and its Great Changehost, among Tzeentch's forces, three of the Stygius Sector's Systems were swiftly taken; with only the Imperium world Mordian being able to resist the Chaos God's invasion. Shortly afterwards though, the light of the Astronomicon, began to miraculously reach the Sector and its beleaguered defenders immediately sent out a request for aid.

When the Imperium received the request for aid, the Stygius Crusade was hastily assembled and sent to defend the Sector, but when it arrived seven sub-sectors had already fallen into Tzeentch's hands. Despite being heavily outnumbered, the Stygius Crusade immediately fought to stem any further losses to the Chaos God's invasion and launched attacks to reclaim the worlds already claimed by Tzeentch's forces. Long story short, the counter Crusade was a long-drawn clusterfuck with Imperium officials being the usual bumfuck retards, the Mordian being such tough bastards to kill and Tzeentchian shenanigans causing mutations left and right.

The Imperium would have gotten its ass kicked if it wasn't for the convenient timing of motherfucking Craftworld Ulthwé arriving in the Sector without warning and began to push back the Chaos God's forces (How Ulthwe managed to escape the psychic pull of the now expanded Eye of Terror is yet to be explained). The Eldar were uncharacteristically pretty damned reasonable and actually told the Imperials on their plans rather than some cryptic bullshit (I guess that Yvraine/Guilliman shipping seem to really took off). They stated that they did not arrive to aid the Crusade against the forces of Chaos though. Instead, the Craftworld's Seer Council contacted the Crusade's commanders and told them they could not save the Stygius Sector and staying there would not aid the Imperium. So Ulthwe ended up covering the retreating Imperials and what's left of the Mordian Iron Guard to safely retreat, regroup and recover.

By the end, 90% of the Stygius Sector fell and Tzeentch manage to carve out a rather big and juicy Sector; most likely thumbing his avian nose at Nurgle over his much larger gains in contrast to the limp-dick three star system of the Scourge Stars.

The rest of Stygius Crusade fleet beat the hell out of town except the Iron Hands said to hell with that, we can hold this shit (and they're no strangers to being stubborn holdouts). So they stayed behind with the Mordians and fought another war for the planet holding the Tzeentch forces at bay until the Iron Hands successor chapters were able to get there and beat Tzeentch off Mordian again. Then the Mordians and Iron Hands and successor chapters start rearming planning to take back at least 2 of the lost systems with resupply from a nearby forge world ready to take the fight to Magnus and his flamers. So, yet again, the Eldar were wrong. Like usual.