Hello my lovely peeps!

First chapter is up!

Okay going to be a simple chapter of just Xero being summoned and some of his legend begin told, nothing too special but i hope you all like it, as this is kinda of a time travel fic, only no one really knows anything. Well someone does know what happens during the fourth holy grail war, but it's not who you think it is, so without further ado, i don't own Rwby or the Fate-verse.

So please read, review and "What the fuc-BOOM"

Chapter 1: The King Of Grimm Is Summoned

The Holy Grail.

A mysterious and highly sought after item by both Magi and normal humans alike, this item has been record as one of histories most desired items since it's legend was told. Funny enough, despite it being relatively young in terms of how old the legend is, it's one of the most famous and popular ones. The legend goes as thus:

The Holy Grail was a vessel used by Christ at the Last Supper. Given to his grand-uncle, St. Joseph of Arimathea, it was used by him to collect Christ's blood and sweat while Joseph tended him on the Cross.

Not much of a legend to be honest, as the story has been told many times before and it's legendary abilities. Such as granting immortality and it's holiness being on par with Jesus Christ, as it was the savior's own personal drinking cup. Many people have made up their own minds up on what it is and what it can do, but to Magi everywhere, it's the answer.

The answer on how to get to the ROOT.

The belief is that is where all magic comes form and is the key to understanding all magic and it's origins. Now how can a holy cup do this you ask? It's simple, as in the years that followed the legend of the Holy Grail, the "Holy Grail Wars" are a ritual that grants a single wish to the victor. To do this, it chose's seven magi's to become masters of heroic spirits, legends of old who died in the past, to fight to the death.

The entire thing is nothing more then a ritual, that requires for the seven heroic spirits or Servants to die(Again) in order for the grail to make it's appearance and only when all seven servants are dead. With this piece of information, one might think the Holy Grail was sentinel and it could think, act on it's own accord.

...And you would be right.

The Holy Grail could in fact think and act on it's own. As it chose Magi who are most needed of it's power, be they a first generation Magi or their bloodline goes back hundred's of years. It could do anything and grant any wish the victor desired, so it wouldn't be that much of a stretch for it to foresee the future. Or at the very least, the future of it's wars.

As such, when it saw the Fourth Holy Grail War, it was not pleased.

Not pleased at all.

To call the war, an absolute hell would be an understatement. In the beginning of the war, the alliance by Tohsaka and Kotomine worked out to a degree. Only for it to fall apart completely when Archer conspired with Kotomine to kill Tohsaka and things just went down hill real fast. Emyia, the man who the Grail favored over all the other masters made every single worst possible mistake he could make and ultimately tried to destroy it, out of sheer spite.

Or maybe it was rage, as it forced Emyia to foresee his "wish" come turn in the most twisted way possible. He even went so far, to defy the Grail that he killed a cognition of his wife and daughter and forced Artoria to destroy the grail itself.

Yes the Holy Grail was not pleased.

One.

Bit.

Each master had his own potential to grow and do good in the world, but Emyia was the one, the Grail wanted to win the most. As, despite his ruthless methods, his heart was in the right place.

That's why it gave him Arthur, so he would win but now after seeing the possible future aftermath of the fourth war...now it had different ideas.

After searching throughout the many different versions of Earth, it found a possible candidate that could not only ensure Emyia's victory, but change the man for the better. Despite not being a legend in earth, he was a living legend in Remnant and the Grail knew, Xero Mazoku would make Emyia change for the better...or he would kill him.

It was a gamble for sure, but this was one it was willing to bet on.

After all, the higher the stakes, the bigger the reward.

Line Break

"This is a bad idea."

Was the thought of one Kiritsugu Emyia, as he and his beloved wife, Irisviel Von Einzbern stood in the church. The Fourth holy grail war would soon be upon them and as one of the chosen master's, Kiritsugu was going to summon his servant. It was only two mouths away and the Magi Killer felt it would be for the best they summon their chosen servant earlier, as their original plans were derailed.

Emyia original wanted to summon the strongest Saber in the world, King Arthur Pendragon himself, to ensure they won this war and bring peace to the world. If not for his sake or his wife's sake, then for his little girl, Illyasviel. The parents knew if they failed then the next grail war, Illya would be the one to fight in it and neither wanted that.

Holy grail wars were hell on earth. Despite how short they were, it was a battle royale of the highest order and no matter what happened, people die. Both fighting and those who aren't.

Back to the matter at hand, the elders of the Einzbern family were more then willing to help him secure victory, by finding a relic that would allow Kiritsugu summon King Arthur. But something went wrong and the relic vanished and they couldn't find a trace of Avalon anywhere. The scabbard was gone and so where Emyia's chance's of winning the war.

Or so he thought.

The elders had found a relic but rather then the one they wanted, they found the King Of Grimm's prized blade the Grand Black Rose. Despite being well over a thousands years old, it was still in prime and pristine condition. It spoke volumes of the time the King lived in, to make such a complex and strong weapon, as they had discovered, the king's blade was some sort of mech-shift weapon.

The man couldn't help but shiver as he remember the tale of The King Of Grimm:

"The world is much older then history could ever say for certain. The world wasn't always called Earth, as before Earth during the age of the gods, the world was plagued with monstrous nightmare's. Creature's of darkness known as the Grimm, the beasts of extinction that hunted man since they came to be. Humanity as a whole was on the brink of extinction, when a hero rose to the occasion to stop them form wiping out all of humanity. His name was Xero Mazoku and he was part of an elite group that could unlock a type of magic, common to the people of his time as everyone had this power. But he was one of the rare ones, as only certain, gifted people could unlock this power and make them more then a match for Grimm. He was the best of the best and if things had gone right, could have been the leader of the group.

"Fate would turn on him as he was betrayed by those he worked with and trusted above all else. While he was on the run form his own people, he was rescued by a hooded figure. It would only be later would he realize he'd been tricked by his worst enemy. For he was twisted and changed by the QUEEN of Grimm and used by her her, to bring about humanity's destruction. For a time he did, till he learned that he was being used and with this knowledge and knowing for a fact, most of humanity would never accept him again as he had helped turn them against one another...he created his own fraction to fight BOTH sides of this war. Despite how high the odds were stacked against him, Xero was clever as he was ruthless. Using their own methods against his betrayers, he turned humanity itself against them and while their soldiers fought each other, Xero slipped through the chaos and killed their leaders.'

"But it was never an easy fight, as each battle pushed Xero to his limits and he used his unique ability to absorb there warriors powers for his own, making him stronger with each fallen warrior. Soon enough he came to fight the Wizard, the man leading humanity and the Witch, the one leading the Grimm. Both fell to his hands and he absorb both of them. That is how he became the King Of Grimm, by consuming the Queen. Using his new found power, he destroyed the Grimm spawning pools and created a new world order. But his work wasn't done yet, as he had to summon the ones who caused this entire mess in the first place, the Gods of Light and Darkness. The fight between the three was legendary and it was only because Xero had an immortal body, that he was able to last as long as he did. However everything must come to an end and after defeating and killing the two gods, Xero died of wounds, his immortally stripped of him by the God Of Light. Xero became a beacon of hope for a new age and to honor his sacrifice, the world was renamed and began anew. With Xero begin humanity's first hero, the one who saved them all form the rule of tyranny gods. It was unknown if he had any children and all those who knew him best, were absorb by him, at their request, so they may continue to help their leader stop the needless bloodshed and death."

It was an amazing tale to Kiritsugu, as he heard it as a child and it brought him hope. As if a mortal man can defeat and kill a god, then maybe gaining world peace was possible after all.

It certainly sounded a lot easier then taking on two gods alone.

But that isn't why he was sweating as he's heard people have tried to summon him before and all ended up dead. As they wanted to use his power for more evil reasons or just simply didn't met his standards to become his master.

"Don't lie to him. Lying is one way to get on his bad side, as he can sense if you're lying. When you feel fear and he asks you if you're afraid, admit otherwise he will kill you. Don't try to trick him, only be honest and truthful, otherwise this war is already lost."

Kiritsugu remembered the words the elder spoke to him, about when he first contacts the servant. Even the tiniest mistake and he could find himself on the end of the an angry Grimm king. But he had to do this, in order to save the world form it's own darkness and to make a better future for his daughter he would do what he had to do.

"Lets began."

Kiritsugu said, mostly to himself as his wife nodded and he cut his palm to began the ritual. The massive blade resting on the alter, began to glow, along with the circle, as he began to chat and intone the words required to summon his servant.

"Here goes nothing."

He thought, as he poured his mana in and said,"I hereby swear."

The circle glow brighter, as the white light began to turn a shade darker,"I will be all that is good in this eternal world."

"Is that so?"

The dark voice nearly startled and broke Emyia's concentrate, but the man pressed on. He assumed this was part of summoning Xero and this was one of his tests, trying to make sure he was worthy of begin his master.

"I shall be the disposer of all evils in this eternal world!"

"Ah yes, how many men have said those same words and how many have failed miserable?"

Once more, Kiritsugu remained focused and didn't let the servants words startle him. No matter what, he would destroy all evil in the world. For Natalia, Mayia, Irisviel and illya, he would do it not for himself but for them all!

"Now come fourth form the circle of binding"

"Hmmmm, alright lets see if you truly are worthy of becoming my master..."

"Guardian of the Heavenly scales!"

The circle went form a light shader of dark, to complete black as red lighting sparked around the church. It made Irisviel duck a bit barely missing the red lighting that nearly hit her and Kiritsugu to suck in some breath at feeling overwhelming pain rush through both his magical circuits! God lord above it felt like acid was rushing through his veins and blood to pour form his mouth.

"Well, well you're still alive? Impressive, very well then you've earned you're reward Kiritsugu Emyia."

The man grabbed his arm, as he didn't even had time to be shocked at the servant knowing his name, as a bright light blinded everyone in the church and the ritual was complete, resulting in a loud:

BOOM

It sent both husband and wife on their ass's and smoke blinded them to everything. As the smoke cleared, the duo were greeted with a terrifying sight. One that had Emyia have one thought go through his mind.

"I didn't summon a servant or a hero...i summoned a monster."

Standing in the middle of the church, six foot tall, with a lean and slender body was a man. He had inhuman pasty white skin, dark glowing red eyes and snow white hair. Angry veins were viable on his face, as his mouth had two lines going up his cheeks and through the middle of them, suggesting he could open his mouth very wide. Two black horns were coming out of his head and curved like a bull's horns. He had bone like armor encircling his neck and two white spiked armor gauntlets going form his wrist to his elbows. His finger nails were claw like, with black painted on them and looked very sharp. He wore a black tank top that showed off his midriff and eight pack abs, along with viable veins on it as well. He wore black pants and combat boots, with a dragon like mask resting on his left hip. He held the large, claymore sword in his right hand as if it was nothing.

"I am Xero Mazoku, class Foreigner. You've survived summoning me, so you are strong and have a strong resolve. Both good traits to have but tell me something, Kiritsugu Emyia..."

The servant silently walked up to the down man, each step echoing throughout the church till he was standing above the two and he narrowed his eyes at the black haired man.

"Why should i call you master?"

Done.

That's it folks, Xero is summoned and Emyia better come up with a good explanation, if he wants to both, live and have Xero help him.

Till next time:

Devil out.