The prototype of Prelati's Spellbook is the R'lyeh Text.
It exists in the Cthulhu Mythos, alongside the Necronomicon, written in the R'lyehian language, and was used by primeval priests and magi.
It is said that it contains a record of how to summon gods from another world.
In the Cthulhu Mythos, R'lyeh is the palace where the Great Old One Cthulhu and his kin lived.
Of course, the grimoire that Caster possesses is naturally unable to summon a monster of Cthulhu's level; at most, it can only summon Cthulhu's kin.
And summoning one is already the limit.
But even if it is just one of Cthulhu's spawn, its strength is still not to be underestimated.
In the anime, that single sea demon was enough to destroy Fuyuki if the other Servants did not block it.
"If Caster really wants to do that, it's going to be a problem..."
Thinking of this, Shirou was about to give an order to Lancer when he heard Caster's almost crazy voice.
"Hahaha, it is finally done... At this moment, I will hold high the banner of salvation!"
In the next moment, the aura of magic was like a churning wave, sweeping in all directions from the direction of the Mion River Port!
...
While Caster was holding the summoning ceremony, the other participants of the Holy Grail War, who were aware of the magical aura released from the Mion River area, began to rush toward that side.
Waver was not the only one who sensed the anomalous magical aura.
The fluctuation of the spell released near the Mion River was equivalent to the multiple chanting of ceremonial spells, the kind that could only be activated by using the magic power of dozens of people.
All the magi in Fuyuki City—in other words, all the Masters who participated in the Holy Grail War—must have felt it too.
Saber, Irisviel, Tohsaka Tokiomi, Archer, and others also began to approach the Mion River.
Saber drove a limousine, and it only took a few minutes for her to sense the place where the abnormal magic aura emanated from the stronghold———— the Mion River.
The old streets of the Miyama district are narrow and complex, and it usually takes more than 30 minutes anyway, but the Servant's Riding skill completely overturned common sense and accomplished this miracle.
The silver-white hull sped through tight corners, its speed breaking through the laws of physics.
As she galloped onto the riverside boulevard, Saber drifted spectacularly to the left and stopped the Mercedes. She jumped out of the car before the gullwing doors were fully opened and sped off toward the embankment.
The fog, which was thick enough to cause ordinary people to lose their vision, had no effect on the Servant's sight at all.
Finally, Saber arrived at her destination.
"Sure enough, as expected, it was Caster."
Getting out of the car, Irisviel, who was standing on the embankment, also stared at the figure in the fog with her magically enhanced vision, frowning anxiously.
Hearing Irisviel's words, Saber nodded in agreement, warily observing Caster's actions.
Caster, unaccompanied by his Master, stood in the middle of the river, as if he were standing on the water.
If you looked closely, you would find that the water under his feet had gathered a large number of terrifying alien shadows.
Judging by the extremely unusual release of mana, there was no doubt that Caster was performing some kind of large-scale magecraft.
The dense fog formed with the river as its source was probably caused by the aftermath of this magical power.
Not only did Caster not chant, but he didn't even appear to be concentrating. He just stood there nonchalantly—from the grimoire in his hand, a steady stream of frenzied magical vortices poured out, and the space around him became distorted as a result.
As a magic furnace beyond the norm, it was also a Noble Phantasm that could unleash magic on its own... If it fell into the hands of a madman, it became an extremely dangerous weapon of mass destruction.
"I have been waiting for a long time, Holy Maiden."
"Huh...?"
Caster bowed respectfully, and Saber frowned, a little confused about Caster's address.
Although she was once a king, and she also received countless kneeling salutes from heroes and subjects, she didn't have any impression of the man in front of her. There was no such man among her former courtiers.
First of all, the title "Holy Maiden" was very strange. When she ruled Britain as King Arthur, she did not reveal her true identity as a woman until the end.
Irisviel, who came down from the Mercedes, hid behind Saber, who was nervously on guard, and quietly watched Caster.
"Saber, do you know this person?"
"No, I don't have the slightest impression of him."
As if hearing the whispers of Saber and Irisviel, Caster looked up and said:
"... Oh, how can you say that? Don't you remember me?"
Saber spoke unhappily in response to his incomprehensible words.
"Anyway, it is the first time I have met you—maybe you have made a mistake. You have mistaken me for someone else."
"Oooooo... oh..."
Caster whimpered as if he was very sad, his hands clutching his hair.
The expression that had been very happy just moments ago suddenly changed dramatically into an extremely embarrassed and depressed look. From this alone, it could be seen that he was a moody and dangerous person.
"It is I! I am your faithful servant, ever faithful, Gilles de Rais! I have been looking forward to your resurrection, and I have been waiting for the day when I will see you again. I have come here for this purpose. Jeanne d'Arc!"
When Irisviel heard the man's words, she couldn't help but open her mouth wide in surprise.
"Gilles de Rais...?"
The Servant who gave his True Name in front of them was already the second to do so. It was unknown what his intentions were, but the name carried a prestige worthy of the present-day Caster.
But for Saber, she just wanted to clear up the current misunderstanding.
"I don't know your name, and I don't know who Jeanne d'Arc is."
Hearing Saber's answer, Caster said, even more confused:
"How...? Have you forgotten everything? Have you forgotten everything that happened in your life?"