This Story Will follow a combination of The Fate and Unlimited Blade Works Routes of Fate/Stay Night, while I have yet to decide when in The Elder Scrolls time-line the events will follow and there may be characters from Tsukihime appearing later down the line.
After Rin removed the vessel from The Grail. She started to run to see Archer, The Alternate Version of Shirou Emiya from a potential future and the man that saved her from having to sacrifice herself.
"Archer!" She yelled desperately running to see him before he disappeared.
As she finally caught up with him on top of a cliff-face she struggled to catch her breath and after regaining her bearings she called his name, while turning to him. "Archer."
"It's a shame really, but it is what it is." Muttered Archer before casually raising a hand.
"Give up on The Grail Rin, At least for now." He said calmly.
Rin was then making a sad expression, to which Archer chuckled lightly.
"Hey, what do you think's so funny!" Cried Rin indignantly.
Archer replied, "I'm sorry you seemed so pathetic I couldn't help myself, I was thinking how we make one sad looking couple."
Rin then asked sadly, "Archer I want you to form a contract with me again, okay?"
"Sorry, but I'm Afraid I can't do that. Besides I no longer have a goal, whether you like it or not it ends here." Said Archer sadly.
"But that would mean, no matter how much time passes I won't be able to save you!" she said after realizing the meaning of his words.
Archer then grabbed her attention, "Rin, You should know by now, I'm hopeless so take care of me, okay?"
"Okay, I'll try to take care of him. I Promise I'll get him to like himself and not end up like you." Rin said to Archer.
"That's good Enough for me." Archer then looked at her and smiled, looking almost exactly like her Shirou.
"Don't worry Rin, I'll do my hardest from now on." He finished as he was close to disappearing.
Rin then surprisingly and unexpectedly, kissed him. Which he eventually accepted before finally vanishing from the current time and place to return to The Throne of Heroes. Rin then turned to see, her Shirou who happily greeted her before they both left together.
After the insane turn of events of The Fifth Holy Grail War, Illya was living happily with Shirou, while being at odds with Taiga and quickly befriending Sakura. Shirou eventually found a way to allow her body to stabilize, so she could live a normal life-span. However as an unexpected and unforeseen side-effect Illya aged rapidly to match her actual-age, as to which she teasingly told Shirou to call her Oneesan from now on, which was very awkward for Shirou to say the least.
Shinji on the other hand, after having a near-death experience at the hands of Gilgamesh and being cared for by Sakura, regardless of what he did to her. Actually began to accept her as a sister and began regretting his previous hatred towards her.
Shirou on The Other Hand followed in his father's footsteps to an extent and becoming what was considered The Second-Coming of The Magus-Killer, while still making time for his family and friends. Even going so far as to kill Zouken Matou and Jubstacheit Von Einzbern in retaliation for what they did to Illya and Sakura for most of their lives.
However nothing could prepare Shirou for what was set in motion without him knowing, as the corrupted grail was destroyed.
At the end of The Grail War
As The Grail was incinerated by a blast from Excalibur, a ripple of magical energy was sent across dimensions.
It wound up reaching a realm full of rocky chasms, where the ground was nothing more than sludge, the sky was constantly burning and the air was below-freezing temperatures. There were countless inhuman monstrosities wandering across the dark landscape, the inhabitants of The World of Nirn knew them as Daedra. But deep in the darkest depths of this realm named Coldharbour, a monstrous being, resembling a gargoyle sat atop a jagged-throne. This creature was known to the men of Nirn as The Daedric Prince, Molag Bal The God of Schemes. He then sensed the wave pass through his domain and muttered something.
"Hmm, interesting." The cosmic horror then smiled sinisterly, revealing numerous jagged teeth.
Back in the present day
Shirou Emiya was walking through the streets at night, when he was approached by a bearded older man with a cane who Shirou recognized as The Kaleidoscope Wizard, Zelretch. Before Shirou could say anything, Zelretch spoke first.
"There is a dark and powerful force coming, that has been interested in our world for quite some time. It does not know pity or remorse and seeks our complete destruction."
Shirou was caught off-guard by the ominous speech.
"Have you ever heard the term, Hell on Earth? That will be Fuyuki if this being would have it's way, be prepared, for a dark-god is approaching."
Then as suddenly as he came, Zelretch had disappeared, leaving behind a confused Shirou, that could only assume something bad was going to happen very soon.
What's up everybody I just had this idea that I needed to start and I'll just post a prologue for now until I catch up with my other stories, I want you to tell me what you guys think of this for now.