First of all, shout out to sUbSoNiCSoundwave, he's the real OG source for this one.

For context if you need:

Archer was summoned into the Holy Grail War where "Shirou Emiya" does not exist. The battle against Lancer at Homurahara ended in a draw as Bazett called off the fighting. With the lack of the presence of the Saber Servant and the Master, Rin had to eat dinner with the devil and visited the most possible Master she knew: Shinji Matou. It was not a pleasant ordeal, however, Shinji understood the weakness he had which was his lack of actual circuits to feed mana to Rider. In exchange for an alliance, Rin had to provide a source of power for Rider through her gems or… other means.

(It's either sucking the mana out of people or the Bill Clinton method of Mana extraction with Archer, you choose.)

Now without the presence of Saber and the Master, Archer had to use his memories to assist Rin in her 'victory' in this wretched war. Without Shirou Emiya to kill, he'd rather use his time here to help the Tohsaka heir out than do nothing. But old memories could only go so far. Without the Bloodfort event, Caster and her Master would not have any incentive to go after Shinji and his servant. Which would mean that Caster would rather dig her trenches and delve deeper into the ley lines on the lofty Ryuudou temple. Making her far too powerful for the Two master alliance to handle.

But like the dwarves who dug too deep, Caster has found the lair of the beast within. And "Fortunately", Archer was there to save her in the knick of time before the disgusting black blood that sprung out of the heart of the mountain. Caster, with 'great assistance' from the red bowman, concluded that something terrible has become of the Grail. She knew what that thing down there was originally - the Greater Grail. But to see its corruption for herself was unnerving even for her. That does not mean her resolve to win it has diminished in any way - well, somewhat if she was honest. So with peace, she kicked Archer out of the mountain.

Archer had relayed everything that happened to Rin. Naturally, she was unamused. Actually, she was seriously pissed. To think that the very thing her father died for had become like that. She wanted to fix it, above all else. But nothing in the texts of her father detailed the procedure to make such a thing because no one knew it was possible! After so many hours pouring into the books, Rin realised that nothing could be done to save it. With saddened eyes but resolved anew. Rin knew she had to destroy it. But how to get that done?

Well, first of all she had to tell Matous. Shinji would go ballistic if she told him alone. She had to tell Zouken too. It's the only way to knock some sense into her classmate. She entered the Matou household with Shinji and Zouken waiting for her at the walkway. Rin told everything she knew. Shinji became mad and accused her of lying, but Zouken knocked his cane into his head. The old man had his suspicions ever since the dubious happenstance of the 3rd War, but now with Rin's news he had all the pieces to the puzzle. So, in a calculated move, Zouken had given Rider back to Sakura - who had been watching in the shadows of the Matou hallway this entire time. Shinji was furious at this. But with 'compensation' from Zouken, he found himself agreeing to it.

And that is where the story catched up. Rin and Archer are now inside the Kotomine church. With a coalition at their back. Archer wondered if all this change happened because of Shirou Emiya's non-existence. But he shoved that thought aside. This moment would change everything, after. His focus is needed.

Now…

Archer stood behind his master. Aloof yet guarded. His outward demeanour is like an iron statue, daunting yet unmoving. He was calmly listening to the conversation between Rin and the Arbiter of the Holy Grail War: Kotomine Kirei. The Grail's integrity has finally been brought into question much earlier than the other timelines he remembers. A significant change from the other ones, that's for sure.

"Kirei." Rin said with sharp eyes. "We can't let the War go on like this. Now that the truth is revealed, the fighting is pointless until this problem can be resolved."

Archer smirks at his master. He was the one who planted the idea in her head, but the execution was all her. To think that she had managed to rally the masters of Caster and Lancer to her cause in just 2 days beforehand was impressive enough. But somehow she had convinced Illya of all people… Now that was a marvel compared to the other timelines. With the power of 4 servants (Berserker is outside) at her behest, surely her words would hold sway.

"Yes, that may be the case. But there is no genuine proof to make your 'truth' into fact." Kirei counter. His back to his pulpit. The apathetic smile and gaze boring into the Tohsaka heir with mild disdain. Archer frowned. And so did Lancer, who spoke up then and there.

"I wouldn't talk to the lass like that." Lancer growled. "And she has a point. What's the point of this war if what we're fighting for is a dirty useless cup? Something needs to be done."

"And that, I'm afraid, is impossible." Kirei explained. "Nothing can be done for nothing could be done. The Grail is too powerful of an artefact to simply be destroyed as you say."

"But doing nothing is worse." Bazett chimed in.

"That, I concur." Kirei deadpanned. "Then let us come together in a vote. All of the masters here can offer a plan of action and whoever's plan gains unanimity will have their plan be the one to follow."

"We all have the same idea." Illya said as she stepped forward from Rin's side. "What else would we talk about?"

"How insincere. You six Masters over there may be united in one cause. But what about the Seventh?" Kirei cryptically asked. His neutral smile had that malicious undertone right then and there. Suddenly, it felt like the rug had pulled from right underneath their feet.

"Seventh? There is no Seventh. I checked the entirety of Fuyuki to know that." Caster declared. Kuzuki beside her narrowed his eyes at the Priest. Something is amiss…

"Then maybe your powers aren't that all it's hyped up for. As expected of you mongrels." a voice from behind Kirei said aloud. Mockery and arrogance coming off of it in waves.

Archer's heart dropped the moment the back door to the church opened. He knew the possibility was there, but that did not make it any less dreadful to see Gilgamesh here. His crimson blood eyes screamed at them for their inferiority. Just like before. But there was a glint of mischief behind them. As if he was doing something that pleases him because no one else but him would get it. Like he was about to pull a trick on them.

"I am surprised that all of you are here. I'd thought that you would all kill each other at this point. But this is just plain boring." Gilgamesh said as he used his Gate of Babylon to take a regal looking seat to sit on. The golden portal appeared as soon as he began to sit down on what would have been air had it not been for said seat.

"Why do you exist?" Rider asked with a frown. "You are clearly a servant, yet you are an Archer class. How can this be?" Sakura, who was standing beside her Servant, could only look with wide eyes at the man she remembered meeting a week ago. To think she was that close to meeting her death without her knowing it.

"Because I wanted to." Gilgamesh answered as if it was the most obvious thing in the world. "After all, being here is much more entertaining. But all of that was ruined because of you." Gilgamesh then glared at Rin with the intensity of a thousand suns. Before he could continue, Archer decided it was time to speak up.

"So you're the seventh master. Is that what you're saying, priest?" Archer asked with a raised eyebrow and a displeased face as he crossed his arms. But there was an underlying tension to it like the other servants. The bowman knew about the previous war and Kirei's and Gilgamesh's role in it. But it doesn't add up. It should be Saber who came out of that door, there couldn't be any other. What is their plan…

"Former Master." Kirei clarified as he walked towards Gilgamesh's seat and placed a hand on it. "I have simply called for the aid of a friend to make this vote as even as possible. How can things be equal when there are six of you against 1, after all."

"Stop wasting our time, Kirei! The longer this continues, the more dangerous the Grail can become for the city." Rin exclaimed in frustration. She then pointed at Gilgamesh and said, "And how did you summon that servant? What are you trying to do here?"

"To think Tokiomi's daughter would grow up to be so stupid…" Gilgamesh said with a sway to his head and shrugged his shoulders as if he expected this already. "I survived the last Grail War, you mongrel. And he didn't summon me. Your imbecile of a father did."

"I would stop your lassie there, Archer. She's looking very red right about now." Lancer whispered to the bowman as the fury of a golden goddess overcame her for just a moment before Archer reigned her in with their shared mental link.

"We are getting side tracked. If you could come out now, please. It appears the patience of our guests is growing thin." Kirei said towards the open door behind him. And with that request came forth two.

And the already high tension peaked at the sight of them. Archer had to take a step back to school his own reaction. As much as he desired it, there was never a possibility that he could ever escape his past. For it always finds a way back to him. In our case, he was wholeheartedly content to believe the notion that Shirou Emiya did not exist. But alas, fate looked down upon him with a middle finger.

For in front of him was the same red headed boy he wanted to kill but thought didn't exist at all. But with a twist, it seems. The boy was wearing a priest's garb. Silver cross and everything. His golden eyes bear that same passiveness and lifelessness that Kirei had but lesser compared to the man. The bowman's eyes went down towards the boy's hand and saw the command seals. All three there. It is clear: he was the Seventh master. Just like before.

Clank. Clank.

"How appalling…" Kojiro whispered from the side. His senses being repulsed from the corrupted magic emanating from the person walking behind Shirou. Medea who was near him concurred. It was a disgusting feeling.

A black battledress of death swished and swayed as the figure revealed herself to them all. From the head to the toe covered by iron armour that littered about her body to protect her vitals. An iron mask of the same colour as the rest covered her face from the others. But that did not stop them from feeling her gaze on them. Like a predator just waiting to pounce on its prey. As she stopped beside her master, she glanced at them with cursory eyes. Examining them with aloofness and apathy. All of them flinched once she looked at them. However, the red bowman did not react the same way. It was instant, but the bowman's eyes and expression showed many things. Realisation, Surprise, Resignation, and finally Pity.

Saber will remember that for later.

"Now that all the Masters are here. Let us begin." Kirei declared.