[Bow] Ciel, originally named Elesia, was born in 1976 to an ordinary farming family in France. She was one of the potential reincarnation vessels prepared by the True Ancestor vampire, Roa.
In 1988, at the age of twelve, she was forced to awaken as a True Ancestor's reincarnation vessel. She became a vampire, her body possessed by Roa, and began an endless slaughter.
Subsequently, she was hunted down by the Holy Church and the True Ancestor Princess, Arcueid Brunestud. After being killed, she resurrected due to her True Ancestor bloodline.
Through studying her, the Holy Church discovered that at the moment of her first death, Roa's soul had already transferred to another spare body. The original twelve-year-old girl was now able to regain control of her current body.
From that point on, Ciel of the [Bow] was born. Possessing a True Ancestor's body and considerable Magecraft aptitude, she quickly rose to the Seventh Seat of the Burial Agency.
After that resurrection, the World came to recognize her as Roa. No matter how many times she died or in what manner, as long as Roa himself was alive, she would always revive.
Simply put, to kill her by conventional means, one had to kill Roa first.
Unconventional methods would require manipulating more fundamental world rules, such as using the [Mystic Eyes of Death Perception] or directly altering the World's rules so it no longer recognized her as Roa.
But... what if the goal wasn't to kill her, but merely to transfer all her Dead Apostle traits to someone else?
"Kirei, is this your choice?"
"I bear her no grudge, and for the past two years, she has been a junior I've come to admire. Why would I kill her? King of Heroes, for you, killing her or transferring her Dead Apostle bloodline to me... are they not of the same difficulty?"
"Kirei, are you actively seeking to betray your Lord?"
"King of Heroes, the Lord never forbids any living being from believing in Him. As Executors, we only eliminate heretics."
"Hmph. Mongrel."
Gate of Babylon, Rank E~A++, contained all Noble Phantasms from ancient times to the present.
With this treasury, the King of Heroes could, in theory, accomplish anything.
And in fact, the King of Heroes did just that. He transferred all of Ciel's Dead Apostle traits to Kirei Kotomine, turning Ciel into an ordinary human girl.
That's why, even after Kiritsugu left and the King of Heroes' seal was removed, Ciel still couldn't climb out of her coffin—though she remained a capable Executor.
Meanwhile, outside the church, Kirei Kotomine—whose head had been blown apart—was fully restored under the immortality rule of that True Ancestor. His eyes snapped open.
At that moment, his eyes were already crimson.
"Heh... So this is what it feels like to no longer be human? How exhilarating. Kiritsugu Emiya, I can't wait to see the look on your face when you see me again!"
Newly resurrected, Kirei naturally felt the urge to feed, but his bloodlust was directed solely at Kiritsugu Emiya.
Turning back, he blasted away the church rubble, his face reverting to its usual impassive expression in the process.
When he reached the basement and threw open the coffin trapping Ciel, he simply looked at the shocked girl and said:
"The anesthetic I gave you will last another six hours. And I believe you owe me a favor. We Executors all know you have two wishes: to kill Roa, and to die as an ordinary human.
"Now, I've made you an ordinary human."
In the coffin, Ciel's blue eyes went still. A moment later, a mix of joy and confusion filled them. After Kirei tore the tape from her mouth, she spoke:
"What do you want? The method to use the Seventh Holy Scripture I possess?"
"No. I've simply gained some extra... human emotions. And it occurred to me that my daughter, Caren, will face an even more tragic fate when she learns of my betrayal.
"Ciel, I want you to take care of Caren. Only I have the right to kill my own daughter. When my wife died, I wasn't able to properly enjoy it."
He covered his face with one hand, his crimson eyes peering through the gaps between his fingers. A twisted smile slowly spread across his dead-fish-like features.
In that moment, Ciel knew: Kirei Kotomine was likely a far more depraved man than Roa.
The Infinite Reincarnator, the Serpent of the Void, one of the original Twenty-seven Dead Apostle Ancestors... yet he was also a former priest of the Church and the founder of the prototype for the Burial Agency.
Furthermore, 1,500 years ago, it was his blood that the priest had used against Camelot.
His name was Michael Roa Valdamjong.
"You..."
"Don't look at me like that. I'm no puppet to be controlled. The True Ancestor you want dead? I'll kill him for you. Little girl, you're still far too pure."
Kirei slammed the coffin lid shut again, leaving the girl—truly only fourteen years old this year—trapped inside.
Meanwhile, at Mount Enzo, Guinevere, the King of Knights, and Irisviel had reached the Great Cavern. They were only waiting for Kiritsugu Emiya to return so the ritual could begin.
"Irisviel, are you truly going to dissolve yourself into it?"
"Guinevere, this has already been decided."
With the King of Heroes' withdrawal, his soul was now contained within Irisviel—or more accurately, within the Lesser Grail that served as her heart.
To summon the Greater Grail, this heart alone was sufficient.
Before Kiritsugu arrived, with the King of Knights and Guinevere standing guard, Irisviel began to inscribe a magic circle. Despite being of the Caster class, Guinevere could only stare blankly at the orthodox magecraft.
She couldn't comprehend it, nor could she be certain if the magecraft's effects would align with her expectations.
Soon after, Kiritsugu and Maiya stepped into the vast expanse of the Great Cavern. Irisviel immediately lay down on the stone altar at the cavern's center.
In that instant, the magic circle Irisviel had drawn began to glow. Then, the cavern floor itself lit up, revealing the massive magic circle that constituted the Greater Grail within seconds.
At that moment, Kiritsugu lit another cigarette. Lying on the altar, having just changed into a white ritual gown, Irisviel could no longer suppress her agony.
"Guinevere, stop the Falsification on Irisviel's heart."
"Kiritsugu Emiya, are you certain? You're killing Irisviel with your own hands."
"But if we want her to merge with the Greater Grail and become the wish-granting core of the Holy Grail System, this is the only way, isn't it? You said that by doing this, the corrupted Holy Grail might be restored, and with Irisviel's will guiding it, my wish could be granted correctly."
Kiritsugu was insistent, and Irisviel was just as determined. If Guinevere tried to stop them before they hit a brick wall, they would only turn against her. Worse, Irisviel might foolishly use the Command Spell—specifically preserved to anchor her soul—to order Guinevere to commit suicide.
"Fine, have it your way," Guinevere said with a sigh. "After you've hit your brick wall, you'd better listen to me."
With those words, Guinevere released the Falsification on Irisviel's body. In that instant, her heart was crushed by the souls of the Servants.
Irisviel died. A hole opened in her chest, and from it, black mud erupted like a fountain, spraying high into the air.
Just by looking at the black mud, everyone present knew it was something utterly ominous.
"Kiritsugu Emiya," Guinevere said, "I'm temporarily transferring Lia to your command. Do you still believe Irisviel can replace Angra Mainyu within the Greater Grail and restore its purity?"
Irisviel was dead, her body and soul devoured by the black mud. On the altar where she had lain, a sacred, radiant cup began to materialize. The black mud that had gushed from her chest now overflowed from this divine vessel.
With Irisviel's death, Guinevere's form began to turn translucent, forcing her to step immediately into the black mud.
In two seconds, the King of Knights' command was transferred. Two seconds later, Guinevere stepped into the spreading mud. Faces of those she had killed—faces she still remembered—flashed through her mind.
At the same time, Guinevere heard Irisviel's Command Spell: "Come to my side." But she didn't see Irisviel immediately; instead, more whispers echoed in her mind.
It seemed Irisviel hadn't lasted even a second before becoming part of the black mud.