Note: Please, do not take this story seriously.
Homurahara is a generic high school you could find anywhere.
Far away from there was a relatively large house.
In one room of that building, Emiya Shirou was awakened by someone jumping on top of his body.
"Gbhhh!?"
"Ah, you have awaken. Good morning, Onii-chan."
She stopped her jumping and sit on his stomach.
"...Illya?"
"Hm? What's wrong, Onii-chan?"
"W-what are you doing in my room? No, more especifically, what are you doing sitting on top of me?"
"I was just waking you up."
"And did you have to jump on me?"
"Well, I can't help it. I took the role of a little sister and I have to act like one."
"What?"
"Just be glad that I didn't ask little brother Berseker to do it."
"... ..."
Shirou tried to process the information. But he'd just woken up, so his mind failed to do it.
"...Anyway, get off me, Illya. What would happen if Saber see us in this situation?"
"Saber isn't here today. Her character changed from your roomate to a transfer student on your class, so you're only going to meet her later."
"Character change? Transfer student? Wait. Wait! I can't understand anything what you're saying!"
"Leaving that aside, Onii-chan. You better prepare to school soon or you're gonna be late."
A battered Shirou ran to the school while holding a toast on his mouth.
Apparently, Fujimura Taiga's character has been changed from 'freeloader and unreliable adult' to 'responsable and mature adult'.
She had been tasked with the duty to cook breakfast.
But there was a slight problem with that: she was a terrible cook. So Shirou just made a toast and left home in hurry.
Fortunaly, he made it just barely in time for school. By then, the bad taste of Taiga's "food" on his mouth was almost completely gone.
Arriving into class, he saw a familiar face.
"Good morning, Shinji."
"Emiya, you being almost late is rare. Did your character got changed to the guy who wakes up late and has to run to school with a piece of toast on his mouth?"
"?"
"Well, I guess that's one of the traits that defines a protagonist, after all."
"? ?"
Saying that, Shinji walked away.
"..."
(What was that? First Illya and now Shinji. And Saber wasn't even in the house.)
"Today is a strange day."
"You say me that."
Shirou turned to the direction of the voice.
"Issei."
"It seems everyone's characters are being reversed or modified to accomodate the new story. Honestly, it's a pain."
"Accomodate what?"
"To be more accurate, a parody story."
"...I still don't understand. In fact, I'm even more confused now!"
"Just make sure to handle your flags well, Emiya. Or else, you are sure to reach a dead end."
"Flags? Dead End?"
Shirou tilted his head and made his way to his desk while still confused.
Looking around, he noticed that the class was more restless than usual, so Shirou asked about this.
"Hm? Didn't you know, Emiya? A new transfer student is coming today."
"Transfer student..."
Didn't Illya say something about this at morning?
...
"I'm pleased to meet you all. My name is Saber."
"..."
"All right. You can sit over there, Saber-chan." Teacher Taiga pointed to an empty desk right next to Shirou.
Saber approached him.
"What are you doing here, Saber?"
"I love you."
Instead of replying his question, Saber boldly said that.
"...What?"
"Whaaatttt!?"
The entire class erupted in chaos.
Sensing an incoming headache and infinite questions, Shirou just asked, "Why?"
"It's the duty of a transfer student character to express their love or interest in the protagonist and shock the entire class on their first day of school. I'm just abiding by the rules."
...
After a hectic class, lunchtime finally arrived.
Shirou staggered to the cafeteria, where he spotted a fidgeting Rin.
"Tohsaka?"
"Ah! Sh-Shirou!"
"Bhwaa!?"
Rin threw something at him.
"I-it's not like I'm doing this for you or anything! I've made too much food and would be a waste to throw it away."
The entire cafeteria was focusing on them.
"And if you don't eat it, I will curse you into having stomach aches!"
Yelling such dangerous words(which was entirely possible for a magus of her calibre), Tsundere Rin ran off.
Soaked and dirty with food all over his clothes, Shirou said,
"What the hell was that?"
Today is a strange day, indeed.
At some point, Shirou had met Assassin the School Gates Guard, Archer the Janitor, Rider the Librarian and Cu Chulainn the PE Teacher.
Currently, he was at the hall, considering to just ditch school and go home.
He wanted to stay away as soon as possible from these goddam lunatics.
"What are you doing outside class?"
But before he could do that, someone had stopped him.
"...What, in the name of all that is holy, are you doing here, Kotomine?"
"It appears that I have been chosen for the role of school's vice-principal. Although I have some complaints about this setting, I have to play the character that I was…ghbh!?"
Kotomine could not finish what he was saying because Shirou suddenly summoned a sword and stabbed him with it.
Laying there, bleeding, Kotomine said: "B-bgh. W-what are you doing?"
"It was just a reflex. Sorry."
He was not looking sorry at all.
...
Emiya Shirou was sent to the principal's office for trying to kill the vice-principal.
"Faker. I've heard that you stabbed... Gwaaah?!"
This time, Shirou didn't summon just one sword. He summoned hundreds of them.
"This parody story needs a conclusion."
Shirou concluded that if a ending is reached, everything will be returned to normal.
And to reach that ending, the main villain has to be defeated.
Emiya Shirou went to fulfill his new objective.
...
Matou Shinji was waiting for him.
Principal Gilgamesh and Vice-Principal Kotomine lay thoroughly beaten at his feet.
"Mwa ha ha ha! Emiya, did you never find it odd that I never complained about the character of an asshole and useless guy that was given to me!?"
He began to explain about his hidden master plan.
Tsundere Rin, Underclassman Sakura and all the School Servants launched a suicide attack, hoping to take down Shinji along with them. But they failed spectacularly and Shinji escaped unscathed.
While they were getting their sorry ass kicked, Shirou wondered.
He could escape. He could just ditch these retards and go home.
But could he really do that?
Could he just pretend that this ridiculous plot twist never happened?
Looking at the defeated and beaten bodies on the ground, Emiya Shirou made a decision.
"No way in hell I can do that."
He will avenge them and stop Evil-Master Shinji's plan.
Their sacrifices won't be in vain.
Emiya Shirou won't cower, even before Matou Shinji's immense power(?).
For he will be a Hero of Justice.
And heroes don't run from their battles.
Now, fight.
Fight in order to protect everyone's smile, Emiya Shirou!