On a barren wasteland of a world a large hulking figure is walking past a gravely wounded space marine who had a sword embedded deep within its chest. He was not alone as surrounding him were the bodies of countless others, his brothers.
Out of the corner of his eye he saw the figure walk towards another of his wounded brothers, his Centurion. The wounded warrior stood slowly and raised his Gladius to the approaching enemy and swung.
Said sword was caught easily within the claws of the figure, it ripped the short sword out of his grasp and reared its claws once more and impaled the space marine, the powered weapon sliced easily through the ceramite armor of the Astarte and punched all the way through. This was the last thing the spectating marine saw before darkness finally took him.
The dark figure walked forward dragging the dead marine with them before dropping them off the edge of the cliff the figure stood back and begin to mutter to themself
"I never wanted this. I never wanted to unleash my legions. Together we banished the ignorance of old night, but you betrayed me, you betrayed us all. You stole power from the gods and lied to your family, your most trusted friends, and most importantly, your own Wife... mankind has only one chance to prosper. And if you will not seize it... THEN. I. WILL."
The Arch-Traitor, Rias Gremory, looked off the cliff towards the massive battle happening. Thousands of Astartes warriors fighting, Brave Saints vs The Sons of Rias, Atlesian Guardians vs Word Bearers, Holy Knights Vs Sacred Roses. It was a blood shed of unmatched proportions, Brother against Brother, Sister against Sister. The Children of the Emperor of man butchered each other with remarkable fury. Titans towered above unleashing the full might of the God-Engines, while tanks and other armored vehicles block out the dirt and Aircraft blot out the sky.
On one planet, Shirayuki the first born Child of Koneko Toujou and first Captain of the Imperial Nekomata swung her blade at Tai Xiao-Long, first born of Yang Xiao-Long, and first captain of the renamed legion, The World Eaters.
The power blades of each warrior collided with a mighty clang, the electrical energy of the glowing blue power sword dispersed releasing a powerful wave of energy. Both warriors glared at each other, one of fury, another contempt.
"In the God-Emperor's name, I must strike you down." Announced Shirayuki. Tai just growled and lunged at his sister.
On Calth. A squad of Atlesian Guardians charge into battle as a Warlord Titan steps near them, they raise up their arms to protect themselves from the incoming dirt and dust that was lifted from the hulking machine's step.
On Nostromo Home-world of the Jäger der Gerechtigkeit(Hunters of Justice) the Jager fights against the oncoming White Fang, which meant brutal Urban warfare on the Hive world. A trio of White Fang Astartes take cover behind a Kratos Heavy Assault Tank, one Astarte peeks around the edge, only to get a bolt shell lodged into his neck.
"From the skies of Terra to the Galactic Rim!"
On Fenris, Home-world of the Space Valkyries. Drop pods of the Phoenix Order are falling onto the world. A few minutes later.
*BLAM*
The pods hit the surface and burst open like a blooming flower and the Space Marines of Ravel Phoenix pour out assaulting the Valkyrie Garrisons as retaliation for the Burning of Prospero, their Home-world.
Somewhere else in the Galaxy a space marine Captain cleaves his opponent in two with a Power Axe.
Elsewhere two Space Marines approach the crater where a great battle between the Titan legions was fought the only thing left now was the molten slag wrecks of the titans and the shells of blown out buildings. And yet they considered this a victory with one of the Space Marines planting a victory banner of the legion.
Nearby titans roam the planet just as the nearby star was setting, looking for their next prey.
"Let the seas boil!" Commands Rias and her sons do as they are told.
On an agricultural world the Dark Legion fires their cyclonic torpedoes onto the planet leaving it bleeding molten lava causing the seas to boil.
On Colchis Asia is walking down the line eyeing her son's preparation for the upcoming battle, all the while she chants hymns and prayers for them.
"LET THE STARS FALL!"
And the Stars did fall, on Terra the loyalist Titans march into battle as missiles and artillery are thrown at them, but they are stopped short by the titans Void shields that glimmer a hexagonal sphere around the titans. All the while Space marines, Tanks and mortal Soldiers swarm under their shadows like ants. Inside a warlord Titan the Princep Hana Song commands her Underlings to work managing damage control, ammunition, and any and all targets. While she herself pilots the War Machine, interred into an Operating Throne. She orders her weapon crew to fire the volcano cannons on to a group of tanks, melting them down. Leaving nothing but glass and scorched earth.
"Though it takes the last drop of my blood!"
More titans show up from behind launching missiles and other ordnance onto the battlefield below.
"I will see the Galaxy free once more!" Rias finally steps into the battle commanding her sons in person. A brave Trio of Imperial Nekomata's rush her trying to bring her down, but she bashes them away easily with World-Breaker. She raises her Clawed left hand into the air as it begins to glow a red energy. A magic circle with her family's symbol grew in the sky. One Space Marine stopped fighting to look up, he gasped and turned to warn his brothers but it was too late. The Power of Destruction, a sacred power only gifted to those of the Bael Clan, came crashing down completely punching through a Titan's Void shield and producing an Explosion comparable to the nuclear bombs dropped on Hiroshima and Nagasaki.
Rias closed her eyes as the explosion happened and opened them as the wind and light died down and she looked on to see a mushroom cloud rising high into the sky, leaving nothing, but a smoldering Crater.
"And if I cannot save it from your failure 'Darling'... Then let the Galaxy BURN!" She announced as the other Traitor Primarchs came to her side. Akeno, Kuroka, Esdeath, Yang, Ruby, Ravel, Asia, and Rem all joined her side seeking personal vengeance on the Emperor and his loyalists in what would become one of the most Brutal civil wars in the entire Milky-Way Galaxy, one where you were not expected to survive. A war so devastating that even in the Grim Darkness of the Far Future, humanity has yet to recover.
The Gremorian Heresy...