The event, which included Pillar Madam Villanelle summoning Excalibur and ultimately leading to Shirou absorbing the weapon, shocked the breath out of not only the two Mages involved in the battle, but also many other figures.
Black, who had been keeping a close eye on Shirou, had almost gasped when the reincarnated Biblical Witch had panicked before sporadically summoning Excalibur — a summoning that bypassed the Bounded Field placed by him using Ancient Magical Script.
However, it wasn't the magic that had shocked the Ad Infinitum, per se.
It was the weapon itself.
Because, before disappearing, the ripples caused by Excalibur in Mana, Life, and Spiritual Concepts in its surroundings had momentarily surpassed the readings recorded by the AI for the Excalibur used by Saber — a true Noble Phantasm!
And that could only mean one thing.
The Excalibur summoned by Madam Villanelle was real — the only one in the Bubble!
Black hadn't forgotten the very first major deviation the Mirror timeline had presented to him, other than Darcie's existence.
It was Madam Villanelle taking Darcie to meet the Six Imperishable Artifacts who made up the Order of the Immortal Lotus by using a Portkey — an Excalibur.
Of course, she had also told Darcie that the Excalibur they used to teleport wasn't real.
The same had been true for the Excalibur used by the Inferius King Arthur at the Thirteenth Circle of Hell.
However, later, what truly had interested Kai had not been the presence of a faux sword-Portkey, or the Inferius's sword, but the name of the Island where the Order of the Immortal Lotus rested.
Avalon.
Combining the separate presences of Excalibur-Portkey, the Inferius's Excalibur, the Inferius's identity as the deceased King Arthur, the several Inferi Knights of the Round Table, the involvement of Merlin, and the name of the Island…
Kai had every reason to believe that if the true Excalibur existed, then it must be at Avalon.
And if that was the case, then such a sword could be nothing but one of its kind.
With the Harry Potter Bubble millions of light-years away from any lore of King Arthur and the Holy Grail, even in the Pillar timelines, if it had an Excalibur, then it must be the only one, unlike the infinite ones in the Fate Bubble.
Unfortunately, with the Six Immortals and Avalon's own defenses, Kai had never ventured in the direction of making Darcie explore his theory.
However, he had always remained prepared for its imminent use by the Order.
Even then, the moment the Ad Infinitum concluded that the Excalibur summoned by the Pillar Witch was not only real but also way stronger than any Excalibur used by a Mirror Saber because of its uniqueness, Black had almost let go of his secret identity to save Shirou.
Almost, because just before taking action, the AI had also noticed the reaction from the Avalon within Shirou.
What happened next became one of the very few events that silenced even the Ad Infinitum.
The Fate Bubble's Mirror Avalon absorbed the Harry Potter Bubble's Unique Excalibur!
Not tear both Shirou and the lesser Divine Artifact within him to pieces, but absorb!
And, as per the Lucky Intuitions, it could only mean one thing.
The Laws and Concepts of the Fate Bubble held a tremendous devouring nature when it came to the Laws and Concepts of the Harry Potter Bubble.
Which, in turn, could also mean only one thing.
Kischur Zelretch Schweinorg hadn't just stripped the Ancient Magical Script from the Harry Potter Bubble, but… He had permanently infused it into The Root!
…
Presently, the moment Shirou absorbed Excalibur, a hiss entered Black's ears, shaking his Source.
Not only his Source, but the entire world was shaking, the seams of dimensions coming apart right in front of his eyes, sucking in the dead souls.
As His creation, Black instinctively knew what was happening, making him frown.
Death the Artificer… was angry.
The entire Bubble shook as the Deep One raged, countless people on the verge of dying meeting a sudden death across the infinite timelines.
His wrathful hisses were so terrifying that even the Pillar Timelines held their breaths.
And, knowing what events had actually led to this utter, damning fiasco, Death's gaze landed nowhere but at the place where the rats who had sold out His Bubble squeaked.
…
A BOOOOOOOOOOOOOOM shook Avalon as if several worlds had collided with it.
Hundreds of Magical Creatures instantly ceased to exist, along with many layers of Bounded Fields that protected the island.
The Phoenix and The Qilin, the two Half Deep Ones resting within Avalon, also shot out of Their nests and stood in the sky, staring toward the Cosmos.
Under them, on the ground, the Six Immortal Artifacts stared in the same direction… terrified.
[Come…] Death's voice was a chill that entered directly into their hearts. [… out.]
[Calm your anger, Death,] the Phoenix cried.
The Qilin also nodded. [Remember the agreement…]
[Agreement?] Death hissed, the sky within Avalon darkening. [You puny parasites… You really think I tolerate you because you two are strong enough to survive against me? … Haha… Hahaha… HAHAHA.]
CRA-CKKKKKK-KKKKKKKKK!
"Almighty above…" the Witch of Endor gasped, the rest of the Six stumbling back a step.
Right above the two Half-Deep Ones, a tear ran through the sky, Magical Laws making up the Bounded Fields getting ripped apart with raw physical power.
And, beyond that black tear, lingered nothing but pure death.
[Have you lost your mind?!] the Phoenix cried. [How many timelines will cease to exist if we exchange blows?!]
[Exchange blows?] Death's voice rumbled like thunder from the blackness behind the tear. [What exchange…]
The Qilin, whose eyes were glowing with millions of stars as He kept looking into the future, suddenly gasped.
Before the Phoenix could understand that, He also saw the thing that could make a fellow Half-Deep One gasp.
From the blackness beyond the tear in Avalon's sky, a blade was taking shape.
It was a curved blade so large that it spanned the entire world.
It was a Scythe, donning blackness like a cloak.
It was… Death.
The two Half-Deep Ones charged forward, screaming to meet the attack before it could annihilate Avalon itself.
And, just as they disappeared into the blackness, the blade fell.
…
Under MACUSA, within the second level of the Yellow Warlock's secret lair, a blade also fell.
The white Bakuya in Shirou's right hand landed on Madam Villanelle…
… opening her from shoulder to waist, her Biblical blood splattering in all directions!