At that moment, Lady Avalon suddenly sensed an extraordinary surge of magical energy. It was...
"Master!!"
Lady Avalon hurriedly warned him through telepathy, but it was already too late.
A scarlet, bewitchingly demonic light blossomed between Shirou and Irisviel.
"What's... going on?"
Shirou looked down and saw something pushing open Irisviel's coat before bursting out through the collar and flying into the air.
It was Caster's Noble Phantasm, the Tome of the R'lyeh.
"What is going on? Why is this Noble Phantasm still here?" Shirou asked in confusion.
Irisviel's face was full of apology. "S-Sorry. I thought you, Shinji-kun, might like it, so I secretly kept it.
"I wanted to use it as a bedtime storybook and read it to you..."
Shirou was having trouble keeping up with this woman's train of thought.
"Hadn't Caster already returned to the Throne?"
Saber looked up at the Tome of the R'lyeh, whose pages were rapidly turning in midair.
Gilles de Rais had vanished without a trace.
Shirou's guess was that the reason his Grimoire had remained behind was that the magical formula he had already cast had not yet finished.
Caster had previously used the Grimoire to open an interdimensional passage for summoning monsters. Even if he was killed, it could not disappear, and could only quietly wait for the passage's duration to end.
However, the Grimoire was now erupting with magical energy far more powerful than before.
In an instant, the countless scattered chunks of flesh on the ground transformed back into interdimensional monsters.
They ignored Shirou and Saber, instead reaching their tentacles toward the Grimoire in the air. Soon, they swallowed it whole.
The tentacles multiplied at a speed beyond imagination, far surpassing anything seen before.
Thousands upon thousands of tentacles intertwined and fused together, gradually forming a small mountain forged from hideous flesh.
Saber was utterly stunned. "Why? Just who is continuously injecting magical energy into that Grimoire?
"How could such an enormous amount of magical energy be possible...? Caster is supposed to have disappeared!"
Shirou narrowed his eyes and voiced one possibility.
"There is only one person in this world who can ignore every condition and forcibly activate Caster's Noble Phantasm."
At his reminder, Saber and Irisviel both widened their eyes.
"Caster's Master... Ryunosuke Uryu!"
In the darkness.
A young man sat quietly on a sofa.
He had maintained this posture for three days.
If he had been a normal human, poor blood circulation would probably have caused his thighs to die, but he was a Corpse-person now, so he had no such concern.
No. Even the function known as "worry" had long since ceased to exist in Ryunosuke Uryu.
He had lost his brain, his intellect, and his sense of self.
At present, he could do no more than make a few nervous reflexes in response to his surroundings. He was no different from a dissected frog in a laboratory.
The young man named Ryunosuke Uryu had died on the day he met the red-haired boy. The thing remaining here was merely a lump of dead flesh wearing his former appearance.
Just moments ago, Gilles de Rais had been killed.
Although the Servant had disappeared, the Command Spells on Ryunosuke Uryu's hand had not. They still clung to the back of his hand, violating the rules of the Holy Grail War.
Command Spells were, by nature, binding curses added by the cursecraft expert Zouken Matou to control Servants.
Anything man-made was bound to have loopholes. Even an old magus with a genius mind was no exception.
He had probably never considered such a situation—
That a Servant's Master could be a Corpse-person.
The innate affinity between "necromancy" and "cursecraft" had miraculously allowed the Command Spells to remain on Ryunosuke Uryu's body.
And that was not the only coincidence to occur to him.
Gilles de Rais had used the Grimoire to open a Soul-Absorbing Barrier in Fuyuki City, transferring the life force stolen from the citizens to his Master.
During that process, Ryunosuke Uryu had also obtained Caster's life force.
Combined with the magical circuits naturally connecting Master and Servant, they achieved a certain degree of shared life—
The lump of flesh, Ryunosuke Uryu, had become another Caster, Gilles de Rais.
That was the truth behind why the Tome of the R'lyeh had not disappeared after Caster's death.
Ryunosuke Uryu, this "dead man," had inherited Caster's life and Noble Phantasm. He was still "alive."
And now, this cold lump of flesh that had long since lost its intelligence performed an action completely outside a Corpse-person's behavioral logic.
"Ah... ah... Master..."
"So frustrating... oh, Master Bluebeard..."
The Corpse-person stared into empty space with murky, vacant eyes, muttering intermittently as he consumed the Command Spells on the back of his hand.
"Kill them... slaughter them all..."
One.
"Unforgivable... must... avenge him..."
Two.
"Master... let me admire something even Cooler... true art..."
Three.
Neither magic nor science could explain where the will driving this lump of flesh had come from.
But it had happened.
If this had been a fairy tale, the phenomenon could have been defined as "a miracle brought about by the power of love."
But unfortunately, Bluebeard was merely a story removed from the Grimm's Fairy Tales for being excessively dark and bloody.
After exhausting all his Command Spells, the last trace of Ryunosuke Uryu's breath disappeared.
He changed from a moving lump of flesh, a Corpse-person, into an ordinary lump of flesh, a corpse. At last, his sinful life had ended.
Even so.
The thing that had once been "Ryunosuke Uryu" still wore an incomparably satisfied smile at the corners of his mouth before his death.
Normally speaking, familiars controlled by magi found it difficult to approach an enemy magus's bounded field.
Therefore, although Irisviel knew that the other factions had sent familiars outside the forest, she had not paid them any mind. They would not be able to discover anything anyway.
But Caster had caused far too much of a disturbance tonight.
Not only had he brazenly entered the Einzbern forest in full view of numerous familiars, he had then attempted to conduct a blood sacrifice and open the gates to another world.
Under these circumstances, it was impossible for the other Masters not to pay attention.
When every participating Master focused their attention on the Einzbern territory, they detected the magical reaction of a large-scale ritual in the forest.
Kenshinnes and his Servant—Demon Diarmuid—happened to be investigating enemies in Miyama Town, not far from the Einzbern forest.
For them, their foremost target was Saber, who had defeated them once before in the warehouse district.
Now that something had happened on the Einzbern side, they could not simply sit back and do nothing. This was the perfect opportunity to take advantage of the situation.
"Can you see what's happening, Lancer?"
The spearman clad in the hide of a demonic boar peered through the thick night fog between the buildings.
"It's Caster. That fool who recklessly barged into the Einzbern forest seems to be plotting something.
"...What astonishing magical energy. With that much power, it would already be enough to destroy this city."
Kenshinnes frowned. "Does that man not know that the Church has issued a wanted notice for him, making him the target of every Servant?"
"If a madman possessed self-awareness, he would no longer be a madman."
Kenshinnes's familiar had just returned from Rin Tohsaka. The Church had just announced:
"Because Caster ignored the secrecy regulations of the Holy Grail War and committed various crimes near Fuyuki City, he has threatened the continued progress of the ritual.
"Therefore, one temporary rule has been added: the Master who eliminates Caster will be granted one Command Spell."
The Einzbern faction had been busy dealing with Caster's invasion all night, so it was obvious that they had not received this information yet.
By the time they learned of this additional rule, the battle would probably already be completely over.
This was a major advantage for Kenshinnes, as it would allow him to take the prize for himself.
He now had only one Command Spell left, and he wanted new ones no matter what.
"Hmph. Let's go."
Kenshinnes set off toward the fog-shrouded outskirts.
"Tonight, I'll make them understand the consequences of opposing El-Melloi... But before that."
With a cold smile, the man asked, "Answer me, Lancer.
"Who is your enemy?
"Is it the evil and insane Caster? Or Saber, who once defeated you and brought shame upon the name of Diarmuid?"
"...What a foolish question."
The black-armored spearman looked back at him deeply before answering in a flat tone.
"There is only one target to kill...
"Saber's Master, Irisviel Einzbern."
For Lancer—Demon Diarmuid—who had abandoned the code of chivalry, the glory and joy of battle had long since become worthless.
Not only that, even the act of swearing another vow against Saber was meaningless.
There was only one thing of value—
To commit every heinous deed in the world by any means necessary, and carve the result of "victory" into the end.
"What's that...?"
Irisviel widened her eyes in disbelief.
Caster continued expanding with unstoppable momentum, already reaching the size of a hill.
Without a doubt, that was the true form of the otherworldly fiend summoned by the Tome of the R'lyeh.
Set against the night sky and towering above the Einzbern forest was the nightmare that ruled the seas of another world—a monster known as the Sea Monster.
The tentacled monsters that had appeared until now in an endless tide were not its kin or offspring. They were merely the tip of its enormous body, like the visible peak of an iceberg.
Fortunately, this was the Fuyuki outskirts, far from the urban district, and no casualties had occurred yet.
But even in the suburbs, a monster of this size could not possibly go unnoticed.
Although it was night in the outskirts, chaotic shouts still drifted over from the distance.
Seeing a scene straight out of a monster movie, it was no wonder the citizens were shocked.
Fortunately, the ritual had also generated a vast amount of thick fog, so the people could not clearly see the Sea Monster's full form.
Before you continue