Fuyuki City, Holy Church.
The late-night chapel was completely empty. Only the candles on the altar flickered in the wind, stretching the shadows of the pews into long, ghostly shapes.
The overseer, Risei Kotomine, stood before the monitoring station in the underground secret chamber, his brows furrowed deeply.
The red wine in his hand had long lost its aroma, but he remained completely oblivious, his eyes fixed dead on the massive crystal ball in front of him.
He had been sitting at this desk for an entire day.
"An Avenger... and a Berserker who failed to trigger the foundation... two Pseudo-Servants..."
Risei muttered in a low voice, his fingers tapping unconsciously on the tabletop.
From the very beginning, this Holy Grail War had exuded an eerie sense of spiraling out of control.
According to the mechanics of this ritual, the appearance of anomalies outside the standard seven classes usually indicated some irreversible damage or mutation within the Greater Grail system itself.
"I must notify Tokiomi immediately..."
Just as Risei turned to grab the magical Mystic Code for communication, the crystal ball behind him, which had been silent all along, suddenly erupted with an ear-piercing hum.
Buzz—!!
The sound was as sharp as nails scratching across a chalkboard, sending a stab of pain through Risei's temples.
He whipped his head around, his pupils shrinking instantly.
The murky surface of the crystal ball had now become crystal clear.
On the astrolabe representing the seven great classes, the Caster foundation—which had previously dimmed due to a failed summoning—was now erupting with a dazzling purple light!
"How... how is this possible?!"
Risei cried out in disbelief. "Didn't the Caster summoning already fail? That Avenger occupied the summoning channel, so the Caster's seat should have been abandoned!"
Trembling, Risei adjusted the crystal ball's perspective. The sensory feed pierced through the church's dome, pierced through the clouds over Fuyuki City, going further and further up...
Finally, it locked onto the stratosphere, twenty thousand meters above Fuyuki City.
"In the sky...?"
Risei slumped back into his chair in defeat, the wine glass slipping from his hand and shattering into pieces.
"Conducting a summoning at that altitude? With a magical energy reaction of this scale, just who in the world..."
Twenty thousand meters above Fuyuki City.
This was a forbidden zone for life.
The thin oxygen, sub-zero temperatures, and violent air currents capable of tearing flesh apart formed an absolute domain completely out of reach for ordinary humans.
At this moment, a massive, streamlined airship hovered silently in the dead of the night sky.
It was two hundred meters long and pitch-black all over, bearing no markings whatsoever, resembling a deep-sea leviathan lurking in a sea of clouds.
The surface of the airship was covered in some sort of optical camouflage spell, allowing it to blend perfectly into the night. Not even the advanced radar of the Self-Defense Forces could detect its presence.
Inside the luxurious observation deck at the top of the airship.
The gravity here was perfectly controlled by magecraft, the temperature was comfortable, and the air was fresh, as if it existed in a completely different dimension from the harsh environment outside.
A petite figure leaned against the massive floor-to-ceiling window, looking down at Fuyuki City, which looked as tiny as an astrolabe below.
It was a young girl who appeared to be only fourteen or fifteen years old.
She wore a gothic-style black-and-white Lolita dress with layers upon layers of intricate lace trimmings.
Her smooth, light purple hair cascaded casually down her back, the tips curling slightly.
She was truly tiny, standing no more than one and a half meters tall, and so light that it seemed a gust of wind could blow her away.
Yet, flowing within those purple eyes was a madness and cunning completely at odds with her appearance, forged through centuries of accumulated time.
"Oh my, my, my. Things are getting really lively this time. It would be a real shame if I didn't step in and join the fun."
She let out a silvery laugh, her voice sweet yet cruel.
The girl's name was—François Prelati.
In secular history, he was the dark magus who colluded with the infamous [Bluebeard] Marshal Gilles de Rais, and one of the masterminds behind the tragedy of Joan of Arc.
But few knew that this notorious alchemist had survived into the modern era by frequently swapping bodies, creating illusions, and utilizing certain special bloodline influences.
And this current shell of a beautiful young girl was merely a minor interlude in the countless pranks of her long life.
"Unexpected! Completely unexpected!"
"A Heroic Spirit that doesn't belong to this world has appeared!"
"How fascinating, truly fascinating!"
Prelati turned around, her bare feet stepping onto the expensive Persian rug as she spun around gleefully like a child.
She casually grabbed a handful of colorful candies out of thin air and stuffed them into her mouth, crunching them loudly.
"That Avenger... hehe, he has a scent on him that makes me want to throw up and laugh at the same time."
"He's very similar to that previous Avenger, yet also like something else entirely... squeezing out the spots that originally belonged to us, hah."
Prelati licked her lips, the purple light in her eyes flaring intensely.
"Since that homicidal maniac boy failed, why don't I just take over this vacant seat?"
She walked to the center of the observation deck.
There were no complicated magic circles drawn there, because for a magus of her caliber, such formalities were completely unnecessary.
In fact, using herself directly as the medium, she simply allowed her Magic Circuits to continuously light up across her body.
"Come, come, the true Caster!"
Prelati raised both arms high. Without chanting those lengthy incantations, she merely extended the most sincere invitation to the void.
"The stage below is already set. There are vengeful wraiths, a maddened knight, self-righteous kings, and the adorable Artoria..."
"What a pity. If only Saber had been replaced by that sow, I could have ravaged her to my heart's content."
"Oh well. How could such a lively party go on without us?"
"Let us thoroughly defile the Holy Grail!"
"Come forth—François Prelati!"
Boom—!!!
The space inside the airship underwent a bizarre distortion in that instant.
Countless slimy, ocean-scented phantom tentacles flashed through the air.
A sense of terror originating from the deep sea, from ancient times, instantly filled the entire observation deck.
Right in front of the young girl Prelati, the air shattered like a mirror.
A pale, slender hand with distinct knuckles reached out from the void and gently grasped Prelati's outstretched hand.
Immediately after, a figure slowly stepped out.
It was a young boy wearing an ornate robe, with short light purple hair.
In his hand, he held an ancient tome radiating a thick scent of blood and an ominous aura.
The book's cover was not made of leather, but rather... specially treated human skin.
Touching it felt as though one could still sense the pain and wails of the skin's original owner while they were alive.
That was the Noble Phantasm—*Prelati's Spellbook*.
The boy's appearance was almost identical to the young girl Prelati, only younger, more androgynous, and bearing that same purely evil smile on his face.
That was the male aspect of François Prelati, recorded on the Throne as a Heroic Spirit.
And also the true Caster.
"My, long time no see, or is it nice to meet you?"
The boy tilted his head, looking at the female version of himself, and greeted her with a beaming smile.