After Shinji Matou's death, Rider, Medusa, automatically returned to her true Master's side.
Sakura Matou.
As for the remaining Masters, Rowan Mercer already knew exactly who they were. Everything had been laid bare inside Kirei Kotomine's memories.
All that remained was simple cleanup.
Find the remaining Masters. Take their Command Seals. Fuse them into his own. End the war in one sweep.
His first destination was the territory shared by Caster and Assassin's Masters.
Their situation was… unusual.
They could be described as one Master and two Masters at the same time.
According to Kirei's memories, Caster's original Master in this war had been Atrum Galliasta, a mage from a newly risen Middle Eastern lineage.
That arrangement did not last long.
Caster murdered him.
She then formed a new contract with Sōichirō Kuzuki, a teacher at Homurahara Academy and Rin Tohsaka's homeroom instructor.
At the same time, using her overwhelming magecraft, Caster forcibly summoned an Assassin-class Servant and bound him under her authority.
Which meant:
Caster's Master was Kuzuki.
Assassin's Master was Caster herself.
A nested contract.
A loophole in the system.
In earlier generations, the Holy Grail War had never been taken particularly seriously by either the Church or the Mage's Association.
When the Three Founding Families created the ritual, they never advertised it as a path to the Root. Only as a mechanism capable of gathering massive quantities of raw magical energy and, as a side effect, granting limited wishes.
The Association sent observers.
They confirmed that enormous mana accumulation was indeed occurring.
That was enough.
No one considered it revolutionary.
From the perspective of elite magi, gathering raw mana was not especially difficult. And those wishes were imperfect. Many things remained impossible.
The Church's stance was similar. They only dispatched supervisors to prevent collateral damage and civilian exposure.
Everything changed during the Fourth Holy Grail War.
One of the Clock Tower's Twelve Lords, Lord Kayneth El-Melloi Archibald, entered out of personal interest.
A magus of extraordinary pedigree.
Most assumed his victory was inevitable.
He did not merely lose.
He died.
That result sent shockwaves through the Association.
Serious investigations began.
And the findings ignited obsession.
The ritual could summon heroic spirits.
Not illusions.
Not imitations.
Actual figures pulled from humanity's collective history.
For magi, this was not about using heroes as weapons.
It was about proximity to legends.
Like historians discovering they could personally interview Julius Caesar, King Arthur, or Alexander the Great.
By the Fifth War, the Association demanded two guaranteed slots.
Those slots became blood-soaked prizes.
One went to Bazett Fraga McRemitz, descendant of the clan tied to the knightly order that once served Cú Chulainn.
Her reason for joining was simple.
She wanted to meet the hero she had admired since childhood.
Kirei killed her before the war truly began.
The second slot went to Atrum Galliasta, who purchased it with obscene wealth.
His goal was to use Caster's magecraft to summon dragons.
When he learned such a feat was impossible in the modern era, his attitude toward Caster soured instantly.
Mockery.
Humiliation.
Treatment bordering on slavery.
When he later realized how terrifying her true capabilities were, fear replaced arrogance.
He contacted Kirei, attempting to have Caster eliminated.
Caster discovered the plot first.
Using her Noble Phantasm, she broke the Command Seal contract, executed Atrum, and fled.
On the verge of disappearance, she encountered Sōichirō Kuzuki.
A meeting that reshaped the entire war.
Rowan stepped out of the Church's shadow and arrived before a secluded mountain temple.
Ryūdō Temple.
"This is the place."
Both Kuzuki and his Servants resided here.
He took a single step toward the gate.
A man appeared.
Purple kimono.
Wooden sandals.
A thin branch clenched between his teeth.
A swordsman stood calmly in his path.
"Sasaki Kojirō," Rowan said.
The Assassin-class Servant summoned using the temple gate itself as a catalyst.
Bound to this location.
Unable to stray too far without being forcibly recalled.
The swordsman's eyes narrowed slightly.
"Master… or Servant?"
"You can decide later."
Sasaki spat out the branch.
Steel sang as his blade left its sheath.
"Tsubame Gaeshi."
Three slashes manifested at once.
Not sequential.
Not fast.
Simultaneous.
One strike became three, overlapping across impossible vectors.
A technique that bent spatial logic through sheer mastery.
Rowan did not dodge.
Golden light enveloped his body.
The three blades struck.
And stopped.
They could not pierce him.
"Impressive craftsmanship," Rowan said. "But insufficient."
He stepped forward and tapped Sasaki's forehead.
A sealing formula detonated outward, locking the Servant inside layered restraints.
Rowan casually tossed the immobilized Assassin into his personal pocket dimension.
The temple gate creaked open.
Inside, Rowan headed straight for Kuzuki's room.
Late night.
One man.
One woman.
Master and Servant.
Adults.
The relationship had long since crossed professional boundaries.
Caster lay with Kuzuki when a voice echoed through the room.
"Dinner's over. Time to collect."
Before either could react, space folded.
Both were erased from the room and deposited into Rowan's pocket dimension.
Clean.
Silent.
Effortless.
Kuzuki was an ordinary human.
Caster, bound to a mundane Master and starved of proper mana supply, could not exert her full power.
Rowan glanced around the ancient temple.
After a moment's thought, he waved his hand.
The entire structure vanished, uprooted and stored within his personal domain.
No loose ends.
No witnesses.
Rowan disappeared into the night.