Hi everyone, this is my first fanfiction, it is a challenge from a friend of mine. I insist on this, it is my first fanfiction so please no flame. I might make some mistakes, and beside this is just a crazy plot bunny that is stuck in my head and that a friend told me to make into a fanfiction as a challenge.

This will be based of Fate/Stay Night Unlimited Blade Works and Transformers Prime, it is set after the end of the TFP series and before the movie.

Again this will be heavily AU so many things will be different.

anyway, the disclaimer, I don't own anything.

Prologue:

A Different Summoning

Shirou's night couldn't have been worst, he had stayed late at school to do some repairs at school, and when he was finally about to leave he witnessed something he shouldn't have. Two strange men fighting one another, one clad in blue, and one clad in red. The blue one with the spear immediately chased after him. And killed him with just one stab of his spear through the redhead's heart,and yet, somehow, he had survived.

Shirou was home and trying to calm down and understand what happened and what had to do. Alas, fate wouldn't have any of that, the boy's eyes widened as he was alerted that someone had crossed the boundaries of the barrier around the Emiya residence. It was that blue spearman again.

After a brief fight that was completely one sided due to Lancer's superhuman abilities and the fact that Shirou didn't even have a proper weapon to fight with,The teenager was eventually cornered in the storehouse. he desperately looked around for anything that could possibly help him, meanwhile unnoticed by both him and Lancer who was about to finish him off ; a magic circle that had been there for years had started to shimmer mysteriously.

"End of the line boy! It is time die once and for all!" Lancer readied his spear making sure to aim properly so his next hit would provoke an instant death.

"No!I refuse to die!Not like this! Not befoe reaching my goal:becoming a hero of justice!" Shirou thought as the blood on his left hand shone a bright red before taking a shape vaguely reminiscent of a sword.

The circle finally activated reacting to the proximity of a master, at first the circle tried to find a catalyst to connect the new master to a servant, but it was disturbed by something, something interfered with the summoning , the circle became purple and suddenly released a blinding light.

Lancer barely had the time to dodge the incoming attack of the newly summoned servant.

"Tsk, really now? The seventh servant! How many more surprises do you have up your sleeves!" He barked angrily as he looked at the new servant.

He a very tall man, at least seven feet tall, muscular without a doubt, he wore a heavy set of armor made of steel that had clearly seen many fights, a purple decepticon insignia was on the middle of the chest-plate. The man's face was square and very angular, he had short silver hairs, a short boxed beard, but the most striking features were his eyes, two glowing blood red irises that shone with malevolence.

The weapon he wielded looked vaguely like a falchion but its blade was jagged and made of an unknown material some sort of dark purple crystal that shone eerily.

Shirou was starting to feel his heart beat heavily in his chest, there was something very wrong with the weapon his saviour had in his hands, it felt evil, he had never felt anything quite like this, he had never thought it was possible that traits like evil could apply to something that is not alive.

The man looked at Shirou with a sneer "I suppose you are my summoner? Make no mistake child, I won't be your disposable tool, though our fates are now tied together, for the moment..."

Then he turned around to face his opponent but choose to instead take a look at his body which caused him to show disgust "Bound to one of you organic weaklings...and forced to assumed the shape of your kind...how disgraceful" he said in a low growl as he readied his sword.

"I suppose you won't accept to call it a draw, won't you, Saber?" the blue lancer replied.

He scoffed "Certainly not, you are a danger that I must end now, I don't want you jeopardizing my plans later...and one more thing, I am not Saber" he replied coldly.

Lancer's eyes widened "Not Saber? Huh you are wielding a sword, how can you be anything else?!" he said shaking his head before taking a deep breath, his spear suddenly was engulfed in a red aura "It doesn't matter, you don't leave me much choice..." then he thrust his spear forward saying two words "Gae Bolg!"

At first it seemed like the new servant had blocked Lancer's attack, but then it somehow hit its target and sent him flying.

Lancer panted heavily and glared angrily as the new servant stood up again "Whoever you are, you are very lucky to have dodged my most powerful attack" he growled angrily.

The servant stood up, part of his chest plate had been torn and a visible bleeding hole was there showing that while having missed anything vital the spear had still hit its target.

"What...was that? A curse...no you reversed the cause and effect to hit me...you humans are really getting on my nerves!" he said anger obvious on his face, he grunted as he got back into a fighting stance his eyes began to glow with even more intensity, they seemed to be burning with hatred, as the warrior had a sudden surge of mana and attacked with an extreme speed and devastating strength.

Lancer was taken aback and barely dodged the attack and put some distance between him and his opponent "Y-you just had a surge of power after I harmed you?...hm so this is what you are...interesting, alas my master is a coward, he called me back since my attack failed...so see you next time...Avenger" he said before running away, or more precisely, jumping.

The now identified Avenger was about to go after Lancer but stopped as he was interpelled by his master, he sneered, he would never accept a puny organic as superior to him, and as such would not call the redhead this.

"Wait, what happened, and who are you?" Shirou asked obviously shocked and confused by what had happened in front of him.

Avenger stared at the boy with confusion obvious on his face "I am the Avenger-class servant you have summoned, you are the one who summoned me right?...of course you are, there is no one else around." Avenger said with a grunt " While you are there make yourself useful and heal my wound" he ordered, he had to set the ground rules as soon as possible, after all he couldn't let an inferior such as that human youngling think he could order him around.

"I-I can't, that level of magecraft is way beyond my abilities" Shirou replied getting more and more confused by the second, and he didn't like the tone the servant used .

Avenger was about to get angry over the lack of usefulness of the magus he was tied to, but he felt an alert trigger in his mind, another servant was approaching most likely with his master. "Looks like there's no time for talking, there's already another servant and their master approahing" He rushed toward the new threat, He managed to corner the master and servant, a tall man in red wielding two swords and a girl around the same age as his summoner, he smirked after hearing the girl calling her servant Archer, while he had swords, it meant that while his opponent had swords, he was mainly a long range fighter and potentially weak in close quarters.

Archer was completely taken aback when he saw this servant, he had expected Arthuria, but instead he was faced by a towering swordman who had absolutely nothing to do with her. Archer was about to change his tactic when Shirou arrived "Avenger stop it!" the youth cried out as the top part of the mark on the back of his hand flashed brightly before disappearing, Avenger gritted his teeth in cold fury as he was forced to obey the boy, that kid was starting to become a bigger liability with each second that passed."Thosaka-san, is that you?" the red haired boy asked before flinching from the murderous glare of his servant.

Rin nodded as she stood up and dusted her skirt. She smiled at Shirou "Well well, looks like we have much to discuss, don't we?Emiya-kun" she said with a playful smile.

End of the prologue

Servant sheet

True identity:Megatron

Class:Avenger

Class skill:

-Avenger A (representing the state of an Avenger as one that gathers people's hatreds and grudges onto oneself. It is easier for one to accumulate loathing and resentment. When receiving damage, mana generation is increased.)

-Memory Correction (People are creatures that forget many things, but an Avenger never forgets)

-Self-Replenishment B

Personal skill:

-Instinct B (Megatron's instinct had been honed through his fights in the gladiatorial pits of Kaon and during the war)

-Charisma B (I need to justify this one? Megatron's charisma allowed him to raise an army to fight against the decrepit caste system )

-?

I hope you liked it and I didn't rush it too much,this is my first fanfic again. . So of course all of you already know Avenger's identity , but nor Shirou nor anyone in Fuyuki know of his true identity hence why most of the time he will be referred to by his class.