Gilgamesh frowned when the black void, that had manifested next to his hip, started to quickly expand and engulf him.

"Well we can't have that happening."

Throwing his hand forward, he used Enkidu: Bondage Chains of Heaven and latched onto Shirou to anchor himself.

Unfortunately, it seemed that he had miscalculated, not taking into account how exhausted his opponent was, which resulted in Shirou tumbling forward, on route to crash into Gilgamesh.

That wasn't part of the plan.

"Wait! Stay where you are!" Gilgamesh angrily shouted, as if he were scolding a disobedient dog

And if he were able to, Shirou would have wholeheartedly obliged, but at the moment had little means to stop himself.

Luckily, Archer was there to save the day, shish-kebabing Gilgamesh's head with an arrow, before rushing forward to grab his alternate younger self- oh wait no, he tripped.

"Oh shi-" was the last thing Archer said before colliding into his younger self and plummeting the both of them into the void.

(Later)

"What the hell did you do!?" Shirou roared, his voice echoing throughout the vast expanse of his Unlimited Blade Works

"Shut up." growled Archer in an equally distressed manner, "I'm thinking."

"Why are you even here? Last time I saw you, I specifically remember you being impaled by fifteen different swords after I stabbed you. Weren't you killed?"

"That didn't mean I was dead."

"That doesn't make sense."

"You don't make sense."

"No you." Shirou glared

"I'm you." Archer glared back

"Grr..."

"Oh, people were right when they said you had homoerotic tension with yourself."

Emiya Shirou and Emiya Shirou swiveled their heads to the sound of the voice, where a bearded old man stood, leaning his weight slightly on a cane.

"Oh no, don't mind me. Get it out of your systems. I can wait."

Recognizing the person in front of him, Archer's face contorted into one of pure dismay, like he had sucked a lemon.

"Fuck."

(Later)

"So boy, how do you like the idea of saving the world?" Kischur Zelretch Schweinorg, the practitioner of Second Magic, offered to Shirou

Shirou, who was confused, made confused sounding noises, "…what?"

"Don't do it. If you are ever going to listen to anything I say, do it now. If you get involved with that deranged troll right there, you'll regret it for the rest of your life." Archer said, his tone deathly ominous.

"You seem oddly concerned for me." Shirou couldn't help but note

"I couldn't give jack about what happens to you. But due to being within a fifty meter radius, I'm afraid that I'll end up being dragged along into whatever nonsense he has in store for you."

"Glad to see you care."

"I don't."

"That was sarcasm."

"I know."

"So have you come to a decision yet?" Zelretch interrupted, "I'll have you know that you don't have much time left."

Shirou cocked an eyebrow, "What, is this some sort of time limited offer?"

"No, I mean in the fact that you only have thirty more seconds before you get ripped apart and torn to shreds inside the void left behind by Holy Grail. And I don't even know why you called it a Holy Grail. If anything, 'Big Evil Meatball' would have been infinitely more accurate." the way the old vampire discussed Shirou's impending demise made it seem like he was talking about the weather.

"Oh yeah, I forgot about that- wait what?"

"I said you have thirty seconds- well now twenty, before you get brutally mangled-"

"Oh-wow! Do you have a clock Archer? Because it is time to save the world!"

"Wait! You stupid piece of uterus poop-" Archer tried to protest

"Ah good! I knew you wouldn't disappoint me Emiya Shirou." Zelretch grinned, "Now, hold on, lemme make some changes so you fit right in with your new world." he then proceeded to twirl his cane and blast Shirou with a beam of energy.

"Gah! Son of a-" Shirou clutched his head in pain as a sudden influx of information crammed itself into his brain.

Chaldea. Animusphere. Preservation of History.

Swords. Noble Phantasms.

He was Emiya Shirou Emiya Shirou Emiya Shirou Emiya Shirou.

"What did you do to me?" Shirou grunted, his voice in a somewhat oddly higher pitch

"Well you have boobs now, for one." Zelretch gestured his hand over his chest and made grabbing motions.

Shirou mimicked the magician, and to his horror, when he reached up to grope his chest, his hand felt the distinct softness a female breast. And to make things worse, he could no longer feel the 'bone of his sword'.

"Now, have fun!" the infuriating vampire gave a thumbs up as he opened a portal behind the red head, before lightly punting him(her) in.

"Oh and don't worry, your girlfriend will follow up after you sooner or later."

Shirou Emiya made strangled screams as she fell into the abyss of space time.

Meanwhile, Archer watched in morbid fascination as the events unfolded, before getting an overwhelming urge to take a nap.

"Dumbass." he muttered

"What are you sitting there for?" Zelretch asked the servant, "You're going as well."

And much to his displeasure, Archer was kicked in too.

I don't really have a great understanding of what the black void thing was in UBW. To my knowledge, it was an aftereffect to get rid of Gilgamesh after Rin and Saber destroyed the grail. If I got the whole thing premise of it wrong, you'll have to forgive me.

By the way, I know the protagonists are not actually Shirou and Rin, just based off them, but I just wanted to explore the idea of 'what if they were?'.

Also I want me a beta. PM if you're interested.