Shirou opened his eyes. He was surprised he was still alive—or by the fact that he was now standing in an average-looking Japanese bedroom.
"How?" That was the first word that came to his mind.
Before this, he had died at the hands of True Archer, Alcides, in the False Holy Grail War in America. He felt it—the piercing Nine Lives went through his chest. It was a pain he couldn't simply forget. A sudden rush of memories went through his head. It took him some time, but he eventually understood his situation.
"Transmigration?" He knew about it somewhat. He did read a little of the isekai subgenre that had been shown to him by his classmates in the past, especially before the 5th Holy Grail War. It was the situation where a person was transported to another world, usually with the main character ending up in medieval Europe. Though this situation was a bit different, because this room was clearly from a modern Japanese household.
The room was full of posters of idols and anime, as well as a collection of manga neatly placed on a shelf. It also had a personal computer that looked far more modern than what he remembered in 2010, paired with a single bed and a two-meter mirror in the corner of the room. He walked toward it without hesitation. He then gazed into the mirror and saw a 1:1 reflection of the younger version of himself. The twenty-one-year-old Shirou was now back to being a sixteen-year-old Shirou, with zero trace of white hair. An innocent Emiya Shirou who was far from the cruel reality of the Holy Grail War, the world, and his ideals.
"I thought it was already bad enough that I joined that war without Tohsaka knowing it, and then I died. She's going to kill me if she finds out about this," said Shirou, despite knowing that he might already be dead after being pierced by that arrow. But of course, that still didn't explain why he had transmigrated.
Using his newly found memories, his name was still Emiya Shirou, with his father still being Kiritsugu Emiya. Instead of being his adoptive father, Kiritsugu was now his literal biological father.
"A new profound revelation... huh."
I improved the flow and readability while keeping your meaning, scene, and dialogue the same. I did not add new story elements.
---
The man named Emiya Kiritsugu was nothing more than an ordinary father to him—aside from the fact that he worked overseas with his wife, his mother, Irisviel von Einzbern. Because of course, it made perfect sense to leave a sixteen-year-old alone in a house.
"Einzbern... Einzbern... Huh, where have I heard that before?" Shirou muttered to himself, unaware that he was in fact supposed to know that name.
He then noticed he was wearing a high school uniform. A name suddenly flicked into his mind.
"Sobu High... man, high school again."
He neither hated nor liked the idea of going to school again, but after experiencing a near-death situation, the thought of attending school was the last thing he wanted.
He was tired.
Leaving his bedroom, Shirou walked toward the kitchen to see if there was anything he could cook. Opening the fridge revealed absolutely nothing.
His eyes then landed on the kitchen table, where a KFC box sat.
Shirou opened it.
Inside were only a few chicken bones and an opened packet of sauce.
"Right... how could I miss the fact that this guy can't cook?" Shirou thought as he glance the memory of his counterpart.
Unlike Shirou, who could clearly cook, this version of Shirou couldn't. As a result, he survived almost entirely on takeout meals and fast food.
Shirou couldn't believe this guy had managed to stay alive like that.
"Sorry, stomach, for having to suffer such cruelty."
He couldn't even fathom the idea of eating like this—let alone every single day.
==
Welcome!" a female voice greeted him as he stepped into the minimarket.
Instead of wearing a high school uniform, he had opted for a simple T-shirt. After all, walking around during school hours in full uniform while clearly not attending school wasn't exactly the best idea.
Emiya Kiritsugu, his father, wasn't rich by any means. His mother, however, was a completely different story. The thick stack of cash in his wallet was proof enough of what that woman was capable of.
He bought several items to properly fill the fridge with actual food, along with the usual hygiene products he normally purchased.
"That will be 6,700 yen."
Shirou pulled a 10,000-yen bill from his wallet and handed it to the cashier. In return, the cashier gave him three 1,000-yen bills and a 300-yen coin.
"Thank you for coming!"
On the walk back home, Shirou realized something.
He wasn't in Fuyuki City.
This was Chiba.
He didn't even know if Fuyuki City existed in this world. Maybe he would try looking it up once he got home.
The city was vibrant—different from Fuyuki, yet strangely familiar. Still, it didn't make Shirou feel out of place. Since the memories of his counterpart had already synchronized with his own, walking through the streets of Chiba felt no different than an ordinary Monday.
He passed by a TV shop. One of the televisions on display was broadcasting the news.
"Uther Pendragon has officially stated that his daughter, Princess Artoria Pendragon, will be the future heir to Britain. In his statement, he said, 'Any public opinion on my decision will not sway what I believe is right. I believe my beautiful daughter is the perfect person to rule this country.'"
Shirou walked past it.
"Ah, that princess is kinda cute too. Good for her," he thought.
The bright blonde young girl shown on the TV did remind him of someone… someone…
"Wait!"
Shirou quickly ran back toward the shop. Pressing both of his hands against the glass window, he leaned closer to the screen.
This was the most shocking revelation he had experienced today—more than transmigration, more than becoming young again, more than everything else.
"S-Saber?"