At that moment, inside the Tōsaka residence, Rin Tōsaka was buried in research.
Books lay scattered across the floor around her desk in messy piles. A quick glance was enough to tell that, aside from historical texts, a large portion of them were volumes on mythology, folklore, and supernatural legends.
As for information on the King of Heroes, Gilgamesh, by cross-referencing what she had uncovered herself with what Archer had told her earlier, Rin felt she had already grasped the core of the ancient king's weaknesses—at least to a preliminary degree.
However, when it came to the other Servant who was just as troublesome—Assassin—Rin had combed through an enormous amount of material, yet still failed to find anything definitive.
That was, until she happened to flip through a book on yokai and monsters and her fingers suddenly froze on a particular page.
One of the Three Great Yokai.
Shuten-Dōji.
Rin stopped turning pages.
Shuten-Dōji—one of Japan's three most infamous yokai—had once reigned as a demon king in ancient times, dominating an entire region.
Possessing overwhelming personal power and commanding legions of oni, this infamous demon lord had been an existence no one dared provoke during that era.
It was only later, during the Heian period, that the great general Minamoto no Yorimitsu, aided by three mysterious elders, obtained the divine oni-poisoned sake and the star-forged armor. By using deception to make Shuten-Dōji drink himself into a stupor, they finally succeeded in beheading him while he slept.
Thus was born the famous legend of Minamoto no Yorimitsu and Shuten-Dōji.
Although Yorimitsu was a renowned general of the Heian era, and his fame echoed through history, the truth was that he had almost never engaged Shuten-Dōji in a fair, direct battle. Victory had only been achieved through stratagems.
As for Shuten-Dōji—the fearsome demon king who once terrorized the land—his death could only be described as tragic and humiliating. To think he would die over a single cup of fine sake, without even understanding how it happened.
Normally, Rin had little interest in legends like these.
The reason this story caught her attention wasn't the tale itself, but the illustration of Shuten-Dōji in the book.
Because the resemblance was uncanny.
The red hair that spilled down his shoulders.
The pair of horns rising from his forehead.
Even that impossibly handsome face.
It looked far too similar to the figure they had encountered at Ryūdō Temple—Ren Kuroda.
As Rin recalled Assassin's hidden title—"a nameless great yokai from a forgotten era"—her certainty only grew.
Shuten-Dōji, one of the Three Great Yokai, was unquestionably a great demon. And given how closely Ren Kuroda's appearance at Ryūdō Temple matched the descriptions in the text, this couldn't simply be coincidence.
"So, Rin… you think Assassin's true name is actually Shuten-Dōji? A famous native great yokai?"
Saber spoke after reading the materials Rin handed her.
"I can't deny that the physical description matches what we saw almost perfectly. But something still feels off. If Assassin really were Shuten-Dōji, wouldn't his true name appear directly as 'Shuten-Dōji'?"
She hesitated briefly before continuing.
"After all, Shuten-Dōji is a fairly well-known demon—ah, no, a very famous yokai. It seems unlikely that his name wouldn't have been recorded in history at all."
"And according to the legends," Saber added, "Shuten-Dōji delighted in devouring young women and children. That clearly paints him as an evil being. But Assassin… he showed clear disgust toward Caster's indiscriminate slaughter. Personality-wise, the two don't seem to match."
When Saber first saw the illustration of Shuten-Dōji, she too had been struck by the eerie resemblance—it almost felt as if Ren Kuroda himself had stepped out of the page.
But after reading the written accounts, her brow furrowed. The Shuten-Dōji described in the legends felt far removed from the Assassin she knew.
Whether Shuten-Dōji was skilled in swordsmanship was unclear. After all, in the legends, the demon king died pitifully—beheaded in his sleep, without ever displaying his full strength.
But in terms of character, Saber felt that Assassin was a warrior worthy of respect.
His martial prowess, his conduct, his sense of discipline—nearly flawless.
Could someone like that truly have been a demon king who once ravaged the land and committed countless atrocities?
"Well, people change," Rin replied casually.
"Besides, Assassin really does resemble Shuten-Dōji, doesn't he?"
"As for his hostility toward Caster… maybe it's because they prey on the same targets—young women and children. Having overlapping 'hunting preferences' might be exactly why Assassin finds Caster repulsive."
"And if Assassin really is Shuten-Dōji," Rin continued, "then it would perfectly explain why he's so absurdly strong."
"In the Holy Grail War, there's another important factor—territorial fame bonuses."
She leaned forward, tapping the book.
"Heroic Spirits come from different eras and regions. When they're summoned to a land deeply tied to their legends, their strength is amplified by the fame they accumulated there. That's what people call home-field advantage."
"Shuten-Dōji is one of this country's Three Great Yokai. His name left a massive imprint here. That alone could explain why Assassin possesses such terrifying magical energy."
"And the form he assumed at Ryūdō Temple," Rin added, "fits perfectly with his legend—it's likely a personal skill modeled after it."
"According to the stories, Shuten-Dōji often appeared as a dazzlingly handsome, cheerful young man to lure unsuspecting girls. That's exactly what Assassin looks like most of the time."
"And the monstrous form he revealed afterward? That would be his true appearance."
Rin held the book in her hands, rapidly drawing connections between the legend of Shuten-Dōji and Ren Kuroda.
The more she compared them, the more overwhelming the similarities became.
So much so that even Saber—who had initially objected—was now beginning to suspect that Assassin truly might be Shuten-Dōji.
"But if Assassin really is Shuten-Dōji," Saber said slowly, "then why is his true name Ren Kuroda? Could it be that Shuten-Dōji wasn't a single individual, but a type of yokai? And Assassin is one such Shuten-Dōji named Ren Kuroda?"
By now, Saber was nearly convinced. The only thing she couldn't reconcile was the issue of Assassin's name.
"Who knows?" Rin shrugged.
"Legends get distorted over time. Either they're exaggerated, misremembered, or outright fabricated."
"But it's also possible Assassin possesses a Noble Phantasm that conceals his true name. Or maybe, as Archer theorized… he's from the future, and no longer the same Shuten-Dōji from the Heian era."
All things considered, Rin was now firmly convinced that her deduction was correct—Ren Kuroda was the great yokai Shuten-Dōji.
And once a Heroic Spirit's true name was known, the number of ways to counter them increased dramatically.
Just like the invincible hero Achilles, whose body became impervious to blades and spears after being bathed in dragon's blood—yet once his name was revealed, his one fatal weakness, the heel, could be deliberately targeted.
That was precisely why Heroic Spirits went to such lengths to conceal their true names.
If Assassin truly was Shuten-Dōji, then even if his weakness wasn't as obvious as Achilles' heel, clues could still be found within his legend.
For instance—the blade that slew Shuten-Dōji, Dōjigiri Yasutsuna.
Or the divine sake that could lull him into a deathlike sleep.
If either of those could be obtained, they would be nothing short of natural enemies to an Assassin identified as Shuten-Dōji.
And even if those artifacts couldn't be found, simply understanding why Assassin was so powerful gave them another option.
They could force him to leave this region.
Without the territorial fame bonus, Assassin's strength would undoubtedly drop sharply—giving them far better odds of victory.
—
Meanwhile, in another corner of Fuyuki City, the very man being labeled Shuten-Dōji—Ren Kuroda—was clutching his head in frustration as he stared at two unexpected visitors.
A man and a girl.
A weary middle-aged man, and a pale, fragile-looking little girl.
The odd pair stood in front of him.
Ren and his group were currently staying in a luxurious mansion within Fuyuki. While its magical energy was nowhere near as abundant as Mount Enzō, the former leyline site…
There was no denying one thing.
Living in a mansion felt way better than squatting in a dilapidated temple.
As for how Medea managed to acquire such a mansion in such a short time—
What? You thought she stole it by force?
Absolutely not.
She had legally purchased it from the original owner—for the exorbitant price of one hundred yen.
The Fuyuki Church was already a hollow shell in name only, so certain insignificant rules hardly needed strict adherence anymore.
Besides, if Medea were the kind of person who followed regulations, she wouldn't have used an illegal summoning method to call Ren Kuroda in the first place.
And thanks to the earnest advice of a certain "people's teacher," she hadn't even killed anyone this time—just applied a bit of subtle mental suggestion magic.
Under the original owner's pained expression, she handed over the massive sum of one hundred yen, firmly establishing that this was not a free grab—the house had been sold "willingly."
It was on the very first day Ren began enjoying his new life of luxury that these two uninvited guests arrived.
And their identities genuinely caught him off guard.
They were Kiritsugu Emiya and Illyasviel von Einzbern—the Master and child of a Servant he and Medea had just "stolen" away.
Kiritsugu had managed to find them because he had taken precautions beforehand, secretly placing a tracking measure on Mordred to prevent that troublesome kid from running wild.
Seeing Kiritsugu again, Ren couldn't help but feel that the man who once wanted to save the world had aged ten years in a single day.
Because so many Servants had been eliminated in such a short time, vast amounts of magical energy had flowed back into the Lesser Grail.
As a result, Illya—once lively and energetic—was now visibly weakening by the hour.
This was the cruel fate of the Lesser Grail.
Once the Holy Grail War ended, Illya's life would likely come to an end as well.
Watching his daughter grow weaker day by day, Kiritsugu—the man who had always dreamed of saving the world—finally understood what he truly desired.
At this point, he no longer cared about the Holy Grail War in the slightest.
Risking his life to come here, he had only one wish.
That Ren Kuroda and Medea would agree to a temporary ceasefire.
Just a little more time—for him to be with Illya.
Kiritsugu knew full well that the Holy Grail War couldn't be stopped.
But there were still two full weeks before its conclusion. As long as no more Servants were eliminated, Illya—though weak—could survive a little longer.
Rin Tōsaka's side, thanks to Shirō Emiya, had already agreed to his request.
If Ren's side agreed as well, then perhaps the Holy Grail War could finally grow quiet—for a few precious days.
Holding the frail Illya in his arms, Kiritsugu was overwhelmed with guilt.
From the Shirō of this world, he had learned that Illya had grown up alone for the past ten years.
Now, as her so-called father, this was probably all he could do for her.
And for Kiritsugu Emiya…
That was enough.