Disclaimer: I don't own the Fate franchise (obviously). If I did, we would've gotten Fairy Knights for Agravain and Mordred.

Fate is a funny thing.

It is intrinsic in the shaping of lives, species, worlds and timelines. Divine Spirits who held authority over it were amongst some of the most feared of their pantheons and even the souls of the exceptional dead would be subjected to it's whims, frequently forced to replay the events that defined their legends when summoned back into the living world. Fate, in a way, could be called a fundamental force of reality in the same way as gravity.

Which made the rare cases in which it was broken all the more interesting, as was soon to be the case of one timeline's Fifth Holy Grail War.

It was over Fuyuki City within a metaphysical plane that the mass of magical energy known as the Greater Grail resided. Within that mass was the being who had once been known as the Avenger class Servant Angra Mainyu. And Angra Mainyu was, for lack of a better term, corrupting.

If All the World's Evils could be described as an exceptionally nasty computer virus, then the Greater Grail could effectively be compared to an exceptional supercomputer with powerful firewalls and multiple in-built safety features in the case that it was infected. Both of which had failed.

With the Grail's failure to successfully defend itself, Angra Mainyu now held complete reign over it and had taken delight in toying with it's functions. The feature that only allowed for heroes to be summoned? Gone; anti-heroes and villains could now be summoned as Servants. The feature that only allowed for Western heroes to be summoned? It was taking a bit of time but it would most likely have something figured out when the Fifth Grail War occurred within a few weeks time. The feature that prevented Servants from past a certain time period being summoned... wait a moment...

Angra Mainyu blinked in confusion (metaphorically that is; they were still currently just a mass of curses) as, for the first time in the decades that it had been stuck inside the Greater Grail, it noticed that failsafe. Taking a moment to examine it, Angra Mainyu had to admit that it was cleverly hidden; by placing the multitudes of other, flashier failsafes and restrictions in front of it, it had been easy to overlook and miss. It was only by mere chance that they had missed it all these years, having not deemed it important enough to look past the other failsafes.

A grin stretched across Angra Mainyu's face (metaphorically, again) as it began to tear it down with all the gusto of a child being given an entire birthday cake all to themselves. The question of why the failsafe was even there briefly crossed their mind before they tossed that thought aside to revel in the further corruption of the grail.

Within minutes, the failsafe was in shambles and shortly after destroyed. Angra Mainyu took a moment to bask in the satisfaction of it's destruction before they took notice of something: the Greater Grail was now absorbing mana from the leylines of Fuyuki at a rapid pace and stockpiling it within seven hastily-constructed separate reserves that were quickly overflowing into and drowning out the rest of the Greater Grail.

If Angra Mainyu had a face at the moment, it's expression would have turned into one that perfectly encapsulated the message of "oh fuck". Before they could even attempt to do anything though, they were swept away in a torrent of mana, dragged off to elsewhere within the grail by the veritable tsunami of magical energy.

As that took place within the Greater Grail, a resulting chain of events took place on a different metaphysical plane. Within the Throne of Heroes, ancient souls long dormant were roused from their slumbers, awoken by the beacon into the living world which Angra Mainyu had unknowingly created. They saw a chance that shouldn't have been possible, to walk the world yet again.

And they fought for it, tooth and nail.

The olden souls of heroes of history, myth and legend, whom had been dragged closer to the Grail's metaphysical location to answer their upcoming summons, unconsciously fought for their very right to be called upon for this Grail War against those more ancient souls, colliding against one another for the chance that their wants and wishes might be realized. They clashed unknowingly, unconsciously dreaming of battles that could never be as they pushed one another aside to claim their spots in the Fifth Holy Grail War.

An ill-tempered survivor snuck their way between the dreams of others unseen.

A blue-haired spearman dreamt of battle against a mountainous beast that shrugged off everything he threw at it.

A fair, statuesque woman dodged the materialized Mysteries of the Horned One.

Hordes of young beasts fought alongside two enemies, forever bounded together, against a beautiful witch.

And the strongest there was fought without restraint against the queen of a world long dead.

By all accounts, the heroes should have won, if not without great effort for some of them. Each of their names were known throughout the world while the ancient souls had little renown to their names. The heroes bore the crystallizations of human worship and legends given form while their opponents bore nameless facts and speculations. The heroes fought with all their conviction to see their wishes realized while the ancient souls fought merely to live.

And it was that last fact that allowed the ancient souls to prevail. For as the newly born AI, their many opponents, the omniscient Daemon King and the Last Master of Humanity from other timelines could attest, the desire to live could overcome anything.

To put it shortly, life found a way.

The survivor quietly reached the beacon without being dragged into conflict.

The body of the spearman was thrown into the distance, broken by the bloodied mountain-beast's tail.

The multitudes of the Horned One's Mysteries forced the warrior woman to abandon further combat.

The witch gave up in annoyance, having come closer to defeat than she cared to by her opponents.

And the strongest there was met their defeat at the jaws of the queen.

With the dreams having met their conclusions, the souls of Cú Chulainn, Medusa, Medea and Heracles quietly drifted away from the beacon and back to their own places within the Throne of Heroes to wait once more. And while their battles may not have left any lasting impression on them outside of perhaps the faint recollections of barely remembered dreams, for the ancient souls their victory was something more. Their will to live had unknowingly rejected and overturned the fated outcome of this timeline's Fifth Holy Grail War.

No more would the boy who wanted to be a Hero of Justice summon a blonde Saber. The survivor would not yield it's right to live to another.

What would have been a fated betrayal would not take place. The mountain-beast's presence would make sure of that.

The adopted heiress of the Matou family would not become a Master. The Horned One had it's own plans.

The strongest of all would not become the Servant of the fairy-like girl. That right belonged to the queen.

This would not be a Grail War between the likes of heroes and villains, knights and witches or good and evil. This was to be a war between survivors, desperately trying to keep their rights to live after having been roused from slumbers spanning eons. This would be a Grail War unlike any other before. Unlike any other after.

This would be a more ancient Grail War.

Author's Note: I tried to make everything seem like it could really happen within the Nasuverse but I don't know if I did that very well. If someone who reads this is well-versed in the Nasuverse lore and notices that I messed something up, please let me know.