The Warp was not a calm place most of the time. In fact, it hasn't known true peace since the Old Ones accidentally tainted it all those millions years ago. But now it stirred as it only did 10 thousand years ago by materium standard, though an infinity all by itself by Chaos' standards.
Grimdark woke to be, at least in the first second of his life, the most powerful God in the warp. Yes, it was an immense change, and this fed Tzeetch second only after Grimdark, as Slaanesh's birth had fed him oh so well. Third, it fed Khorne, for he did not care from whence the blood flowed, only that it did, and in truth, Grimdark did not feed on blood or violence, but on resolution. And then there were the losers. Slaanesh had already lost a quarter of his ten millennium struggle and was continuing to lose ground and color, his oh so beautiful color. The Emperor's Children - Gods he didn't know whether to hate that name or amuse himself more that he stole the Emperor's best and favorites - were the only ones truly driven out of their former lands and of Grimdark's ever expanding empire. Chrone worlds were absorbed into Grimdark's Eye, the suffering of the countless Eldar souls abruptly stopping, being replaced with the suffocating resolve of the new God. None knew yet what this would entail, but many of the lost and damned souls actually started thanking and worshiping him. He somehow answered in half-formed images and words that if they wanted to do so, they'd have to resolve themselves to his path and the path of literal darkness, not just metaphorical. To ignore pain and suffering, even their past if need be, and look into the future. Not for hope, not for their people, but for Him. Not even He was sure what he was doing, but he had seen enough of the Others' Empires to know he should at least build his own, and to learn from Slaanesh's mistakes and not try to take them all down, but consolidate what he had.
He felt a sort of happiness, if beings dubbed Ruinous Powers could feel that, of the resolve of those that decided to join him and consolidate his new realm with the fervor of zealots that only the Word Bearers and the Imperium could bring out of men and creatures.
And as the landscape started to change, so did loyalties. From lower Daemons to Daemon Princes, many flocked to this new domain of darkness, without fear that it would consume them. And the former mortals followed, as their superhuman brothers in the Imperium started the trend.
Mortarion and much of his Legion had been made to remember in the moment of the Corpse Emperor's lackeys' flight of their current status, how they were corrupted without their volition by a sadistic entity that claimed to love them, but did its best to break them. They realized they had only left one decaying False God to be brought to their knees of another, one possibly worse than the Emperor. They deserted their Papa in flocks, almost all but the most indoctrinated and "lovable" Death Guard rushing to their stalwart new God. There was someone who understood them, who understood the true meaning of steadfast, of why they had to leave the Imperium that was already in shambles, of how to consolidate their position, and Mortarion liked the association between his Grim Reaper image and the grimness and darkness of this new entity.
The Iron Warriors, normally unaffiliated with Chaos, also recognized the strong will of Grimdark and over half the Legion converted in worshiping him, some still reticent that he still may be a darker facet of the False Emperor, others refusing to side with their centuries-long former enemies, the Imperial Fists. Still, it was a great and high tally that Grimdark had reaped from a normally neutral faction.
The Word Bearers rejoiced in the birth of a new God, but were content with watching from the sidelines and continuing to worship Chaos Undivided, but some of the smarter and more gluttonous warlocks in the Legion were already making deals and learning new magics and techniques of pure darkness not minutes after the giant's birth.
Malal lost half his support exactly on this new God's birth, as those that worked for him without worshiping saw an opportunity to strike at the "old regime" and saw how Malal was so self-destructive that he'd drag them down with him, accomplished revenge and hate or not. Malal was furious, but had enough enemies as it was and now risked losing himself completely, almost being destroyed utterly as he came under the scrutiny of laughing brothers.
But the most surprising and unexpected addition to Grimdark's new realm was the one he had to actually work for, in a manner of speaking. He was old, and tired, and bitter, far different than the idealistic shapeshifting father's son and builder he used to be. Magnus stayed on his obsidian throne in his obsidian tower watching this new turn of events with an almost uncaring eye. He noticed that his master seemed nervous somehow, as though the strands of fate were going against his plans. Magnus looked lazily at the incoming darkness to his realm and stared impassively into it. The darkness made no provocation against him or his sons, and Magnus took it as a good sign. Grimdark did not talk to Magnus as humans would, but through images and memories of the former. He showed all of Magnus' follies, how he was duped, how he had tried to destroy the Space Wolves - or save them? or his Father's Imperium from them?(1) - not even Magnus knew even then, nor now, perhaps not even Tzeentch - , how he had run from fights his whole life, yet this new God still had hope for him. Now Magnus had matured, now he could see - hopefully - staying his ground and fighting for what he believed in was the best course of action. Grimdark proposed Magnus to join him along with his Planet of Sorcerers, and that he would pay a price, of course. His entombed sons by Ahriman would be released, while their unrelenting shells would be replicated so they'd always serve their former prisoners. In return, Magnus was to stay against any threat, and never back down from a fight unless the bigger picture demanded it. Magnus considered, sighing at the need to make another deal with a Daemon, - a construct, for the Great Ocean's sake! -, not even birthed like his sons from mother and father, but having been promised his lost sons' return with so little asked, he reluctantly agreed.
Other than these, Greater Daemons and Daemon Princes from all the other Gods came to him, mostly from Khorne who saw a good place to battle and advance now that their lord was if not descending, at least stagnating, and from Tzeentch, who saw the potential for change and risked their master's eier and loss of knowledge from him for the opportunity to change theirs and others' futures. But of course the Great Betrayer didn't hold that against them, even deciding to lend them a hand from time to time so they'd tangle the web of lies and madness oh so even more beautifully. Even some Daemons of Slaanesh tried to get in on the action, but were pointedly refused, on the grounds that they were really fickle things who cared not for standing against odds or tarnishing themselves, but for their looks first and that their ideals did not match with Grimdark's character. The few allies and spies he could have gained from Slaanesh's camp were thrown away through this, but of course, the new power did not care for that.
It had and would continue to acquire eldar, after all.
It wasn't only the human empire that was hit by this powerful blow. As much as in some ways the Imperium had created its fifth God quite unexpectedly, Chaos has never cared about which race it would corrupt or would rule the material universe, as long as bloodshed, hope, betrayal, death and assorted sins and emotions would prevail. Grimdark was not the Emperor reborn as a God. He did not care if the grim defenders of his realm were human or xenos, only that they fight the impending horrors of the Universe side by side forever. Nor did it care about their reason, being to protect their families, their species or they own lives and futures, only that they did so.
The Eldar, despite millions of years in learning to manage their tides with the warp, were once again unprepared. The issue, was, of course, that they had prepared for straying thoughts towards lust, not righteous anger towards their Great Enemy. Not against the sorrow of loss and the will to move on. After all, all these thoughts, feelings and ideas had helped stave off the enemy they knew. But new creatures were born in the warp all the time, and as they grotesquely and exagerratedly mimiced the physical universe's inhabitants' ability to adapt to niches and attack or defense mechanisms of both their hunters and pray.
And there was much grimness, darkness, despair and hopelessness, but also resolution in many an Eldar's hearts. When the tide came, they didn't scream, they didn't yell, not like their weaker brothers that almost lost their bodies and minds to the psychic scream of a new birth. Instead, they just upped and left, taking advantage of the lack of cohesion in their brothers'. They knew now that their only hope for the future was not a never-to-be-born god of their own - or too-late-to-be-born anyway - as one was born right now. One willing to gather all who accepted It from all races and fight until the end of time so their kin would not have to. One that saw how they embraced darkness so that others would not have to. One that would fight against any and all odds, even if at the moment it was one of the strongest creatures in existence. One that did not delight in their suffering, or even in its enemies' suffering, but was only content with giving power to those that would not turn away, not even against the (other) Ruinous Powers. A tempting offer that many succumbed to.
In Commoragh, many an Archon found themselves without their Incubi, who left for their temples without a word. The temples are rumored to now be under the sway of Chaos, its wraithbone now of an obsidian color, marked with the eight pointed star and interestingly what apparently looks familiar to the Imperial Mon'Key's heraldry skull. When hearing this, Vect himself is said to have secluded himself for seven days and seven nights to ponder this new factor into his vile equations.
There was also grim determination in the Tau's ranks, but fortunately for them, their worlds were blissfully unaware of most horrors and fights through their Empire. Though half the warriors left, the civilian population was mostly untouched. It is rumored that soon after these events, Farsight's Enclave has become both a bastion for the refugees from the Tau Empire, the Imperium of Man and other xenos races until then unheard of even by tau or man alike. Any plan of the Tau to bring the Enclave back into its fold has been postponed indefinitely, especially with the worrying reports gathered from "advanced scouts". They claim Farsight's capital is now a pitch black fortress with runes similar of that used by the barbarian gue'vesa raiders, though with little in the way of the barbarian behaviour associated with the users of such vile icons. Instead and in contrast with Empire worlds, they look more like the human Imperial's worlds, dark, gritty though not dirty, and most of its citizens droning away without appearances of many personal joys or even physical light in most places. Despite that, they appear to have leaped technologically, Dark Mechanicus adept being spotted amidst the locals, deformed abominations that were thought until then incompatible with the Tau Empire's Greater Good, obviously somehow subdued or enticed by Farsight to join his cause.
Author's Notes:
(1) I'm referring to the Battle of the Fang, where Magnus stopped a Space Wolves apothecary from removing the gene-curse that forced Space Wolves to stay close to Fenris less they get corrupted. The future the Apothecary had in mind though... was not well received by many in his Chapter and there were implications that if he had succeeded, the Space Wolves would've taken over the Imperium and made the worst fascist state we know as the Imperium today look the 21st century's best democracy. It is somewhat implied that Magnus destroying the cure probably saved the Imperium from something worse.
Review answers:
Master of the Boot: Thanks for the reviews and I'm glad you see almost exactly where I'm going with this.