Disclaimer: Don't own Warhammer or Fate/Stay Night.
Throne of Heroes 40,000
Within the Golden Throne upon ancient Terra the God Emperor of Mankind slept. For ten thousand years his spirit had watched over humanity, holding back the ruinous powers and lending what aid he could to his warriors, even as he lay crippled.
But at long last his strength was failing. The Necrons and Tyranids swept inexorably across the galaxy, the Orks massed more and more frequently and the armies of Chaos maintained their relentless assault against the ever weakening Imperium. For all he was called god even the Emperor could not fight on so many fronts at once.
One option remained however: The Throne of Heroes. A multi-dimensional archive containing the greatest heroes of humanity. If he could open its gates and call upon those within humanity may yet survive to see his reincarnation.
Such a plan was not without risk. To access the Throne would leave him vulnerable and cost much of his remaining power even should he succeed. But as they had once said, desperate times...
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Across the Imperium psykers cried out in horror as the Astronomicon, the very essence of the Emperor's might, died. Ships wallowed in the warp, lost and helpless. Combat caster felt their wards crumble as the host of demons clawing at their minds redoubled. The Eye of Terror pulsed and bulged.
For long minutes the Imperium trembled. Fearing that their Lord had, at long last, succumbed to the inevitable.
Then! With the same suddenness it had failed the beacon of divine power returned. Weaker than it had been, but carrying an emotion long absent from the Emperor's soul song: hope.
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Almost unnoticed in the wake of the Astronomicon's return another power had come to the galaxy. Figures, armed with ancient weapons and armour, appeared on worlds throughout the Imperium. Cadia, Armageddon and dozens more worlds besieged by the enemies of man.
Humanity had called for aid... and the heroes of the past would answer.