The sacred mountain where dragons once nested in the past—Mount Enzou.
Although the truth of this legend was unclear, from a mystical perspective, Mount Enzou was indeed a gathering place for rare ley lines. The three main ley line convergence points in Fuyuki City—Fuyuki Church, the Tohsaka Residence, and Mount Enzou.
Among the three, the level of Mount Enzou was the highest, and therefore, Mount Enzou was chosen as the best place for the Holy Grail to descend. Even the Greater Grail's circuit itself was placed in the large underground cave on Mount Enzou.
Although they were in a different world, fortunately, the path to the large underground cave was no different from what Naoki knew. After walking for some time following the path in his memory, he and Gray entered a silent and deep mountain passage.
[This cave... was it formed naturally?]
Add looked around curiously.
[It's really strange for such a mountain passage to form. It's usually impossible for humans to do it. Could there really be dragons nesting in this mountain?]
"Who knows? Aren't Phantasmal Species like dragons supposed to have long since moved to the Reverse Side of the World? The dragons that still exist on the outer side of the world now should only be Albion under the Clock Tower. Although that's already a corpse."
Naoki said that, but in fact, he was also a little curious about the truth of the legend of Mount Enzou.
'Sajyou Manaka, is it true that there are dragons nesting here?'
[...]
No answer.
'Manaka?'
[...]
'Still locking yourself away?'
Don't talk to me, you perverted vixen, the only one who can talk to me is the Prince—such a thought suddenly reached Naoki's mind.
Naoki frowned.
'You said not to talk to you... but weren't you very actively taking the initiative to talk to me before?'
[Go die]
"This girl is really strange."
"Eh? Big Brother? What did you say?"
Hearing Naoki mutter, Gray immediately turned around and asked curiously, "Is there something strange about me again?"
"No, not you, but this guy." Naoki patted his chest, "I wanted to ask her if it's true that there are dragons nesting here, but she ignored me, even told me to die, as usual doesn't like me."
[There's nothing to talk about with you]
'Didn't you say you didn't want to talk to me?'
[Ugh—you vixen die a thousand deaths!]
'I told you not to shout loudly in my mind!'
Massaging his aching temples, Naoki sighed helplessly: "Hah, forget it, whether there are dragons nesting or not doesn't matter. After all, coming here this time wasn't to kill dragons anyway, just to set up some traps."
While speaking, the mountain passage had reached its end. The narrow and dark path instantly widened into a huge underground cave, and strangely, although it was underground without any light source, the environment inside the cave could be seen clearly.
And in the middle of the large cave, there was also a round platform like an altar.
"This cave was formed naturally, then the platform was built by humans afterward?" Naoki walked to the platform and squatted down, touching it, "Such a strange environmental construction, either all made by humans, or all influenced by nature, neither seems possible."
[Maybe. Do you care about this place so much?]
"A little."
Naoki took out a small red gem from his pocket and inserted a little Mana. After a flash of light, the gem turned into a red orb.
It was a Logos React.
Seeing Naoki place the Logos React on the ground, Gray unconsciously felt confused: "Big Brother, what are you..."
"The core of the Holy Grail War—the Greater Grail—its circuits should be buried beneath here. I'm a little interested in the Greater Grail's circuits themselves."
Putting aside the function of granting wishes in a distorted way, the Holy Grail was essentially just a huge source of Mana. Because the Mana accumulated in it was too great, it could manifest wishes. What interested Naoki wasn't the wish-granting machine function, but the Holy Grail's function as a Mana source.
He had already decided the function of the Logos React—using it as an autonomous combat puppet that could freely change shape, so that basically he himself would need to bear the Mana for two people.
But this wasn't completely autonomous. Once Naoki's Mana ran out, the puppet would stop operating. And if he used the Holy Grail as a Mana source...
"Eh?"
The information sent back by the Logos React made Naoki's thoughts suddenly stop.
It turned out... there was nothing?
The stone platform beneath it, according to the results, was actually just an ordinary stone platform? Although there were indeed some residual Mana reactions, they didn't form a complete circuit scale at all, let alone the Holy Grail circuit, at most only the size of breadcrumbs.
But how was that possible?
Wasn't the Holy Grail circuit inside this large cave? Naoki was sure his memory wasn't wrong, but the results of the Logos React scan couldn't be wrong either.
"Meaning, the Holy Grail... disappeared?"
'Could it be because of Miyu's arrival, the underground cave spaces of the two worlds swapped, causing what's here now to be... no, that's impossible, the underground cave on the Ainsworth Family's side also has the Holy Grail circuit, this is the same in both worlds.'
But why? Why did the Holy Grail circuit that should have been here disappear?
"Ruby, ask something."
[What's wrong?]
"Ten years ago, in this city, did a Holy Grail War ever happen?"
[Holy Grail War? Doesn't that happen every so often?]
Ruby said somewhat confused.
[Almost ten years ago, information about the Holy Grail War suddenly spread in the world of magic. Because it was the most likely way to reach the Root at the time, most Magua started holding subtype Holy Grail Wars like crazy, although the scale wasn't as large as Fuyuki's, most were battles of two to five Servants]
Subtype Holy Grail War?
"Are you sure?"
[Sure, in fact, our arrival in Fuyuki City this time was also for this reason. On the surface it was to collect Class Cards, but actually it was to investigate whether the Class Cards were related to the subtype Holy Grail War, and to confirm whether the regular Holy Grail War originating from Fuyuki City might be held again—but now it's confirmed that there's absolutely no connection~]
Ruby's answer left Naoki silent in thought.
The vanishing Holy Grail, the subtype Holy Grail Wars that frequently occurred for more than ten years...
"Ruby, the last recorded regular Holy Grail War that occurred in Japan, how many years ago was that?"
[Counting now, it was almost seventy years ago. It's said that even the German army interfered at that time]
Seventy years ago, the German army interfered.
'So that's how it is.'
This world wasn't just the Magical Girl Illya worldline. Magical Girl Illya was just a large branch of this parallel world. Its core was actually—
"Fate/Apocrypha... huh?"