Hassan of the Cursed Arm wasn't a Servant that had shown up in the Unlimited Blade Works route, Black knew.
Unlike most of the Random Worlds, the Fate Bubble was notorious for having an enormous number of timelines that behaved like the main storyline.
Unlimited Blade Works and Heaven's Feel were just two of the main storylines centered around the Fuyuki Holy Grail War.
Normally, the Grail had the rule of summoning seven Servants of different Classes.
These seven Servants fueled the magical energy channel, opening a path to the Root and letting the Grail grant wishes upon their death.
Of these Classes, seven Classes were most prominent — Archer, Saber, Rider, Assassin, Berserker, Lancer, and Caster.
Among these, the Assassin Class still stood out, despite not being as strong a Class as Archer, Lancer, or Saber.
The word assassin itself had taken root in the Holy Grail, getting attached to the mythical figure Hassan — the leader of a group of assassins from the legends.
Now, no matter when an Assassin was summoned, the Grail always summoned a Hassan.
Also, as Hassan was a title, not a name, all those who had remained a leader of this group of assassins in the past remained a choice to be summoned by the Grail.
Oddly, in the general route followed by the Unlimited Blade Works storyline, it was Caster who had broken rules, summoning an Assassin by herself before any Master could have done so.
It had resulted in the Grail bringing forth a fake Assassin, who hadn't been Hassan, and whose existence had been tethered to the Ryuudou Temple.
Things obviously had taken a much different route now with Black's intervention.
If it were any other Bubble, such blatant meddling with the storyline events would have attracted Timeline's wrath by this point.
However, two factors helped Black avoiding such an unwanted outcome.
First, the current timeline was a Tertiary one, i.e., it was only a Key Timeline.
It had nothing to do with the events that happened before and after the Fifth Fuyuki Holy Grail War, even though it gave the impression of having a long past.
Second, all Fate timelines remained in a constant state of diverging from their general Routes.
So, bleeding, Black looked at the Assassin and knew the Unlimited Blade Works Route was already transitioning to a distorted Heaven's Feel Route in this timeline.
The moment Justeaze had uttered Sakura's name to him weeks ago, this was bound to happen, anyway.
"Hahaha!" Zouken's laugh buzzed across the Grand Hall along with chirps of insects. "To come here… Should I consider you brave or a fool?! Did you really think I wouldn't recognize your nature, creature?!!
"Others might not know, but I have spent hundreds of years observing the Einzberns. I know their history, their schemes, and their desires better than anyone because I was with them. There can never be a male Homunculus from the Einzbern family.
"It's not a flaw that they can just rectify with research. It's related to the Root itself. And that makes you… a cheap copy. Kill him!"
Assassin's face was hidden behind a skull mask.
Suddenly, it twisted its neck, an annoying chatter echoing out of its mouth.
It threw open its dark robe, showing its right arm. It was long and bandaged. As it lifted the arm, it began glowing from within, as if the bandages were wrapping lava itself.
Noble Phantasm —
With a bang, a massive, demonic arm tore through the bandages and shot toward Black, the entire hand glowing bloody red.
— Zabaniya: Delusional Heartbeat!
Assassin's right arm belonged to a Demon, and it held the Curse of Death.
By merely touching the chest of any lifeform, the Assassin could create a fake heart within the palm of the cursed hand. Then, upon crushing the fake heart, the real heart will also get crushed.
As simple as the Noble Phantasm sounded, it was potent enough to one-shot even a Heroic Spirit.
Even Black, who didn't fear getting his heart crushed, was bound to lose Quality under the added effect of the Grail, Root, and the Fate timeline.
Swishing across the hall, and within a fraction of a second, the cursed arm reached Black.
Suddenly, two red-glowing swords struck the hand, bouncing it back, the sound of steel kissing steel ringing in the surroundings.
A bronze-armored figure, wielding two longswords, materialized next to Black.
Red and black vapors were rising off the knightly existence, two massive cylinders propped on its shoulders, having a blue-specked green solution.
It was Petyr the Bronze Titan.
Zouken Matou didn't know what kind of abomination Petyr was, though.
"Berserker?!" Zouken wondered aloud. "How can it be?!!"
Petyr didn't hold any Mana. Hell, he held nothing. No matter how much of a grand mage Zouken was, even he couldn't unravel Petyr's mystery.
Zouken knew one thing, though.
Black hadn't arrived at the Matou Mansion with a Servant.
That's why he had attacked Black, unleashing the Assassin, to begin with.
A boom rang out as the cylinders pumped the reinforcing solution within Petyr, the floor cracking under his feet. In a blur, he disappeared, appearing right behind Assassin.
The ear-ringing sound of steel striking daggers took over the grand hall, sparks blinding eyes here and there.
Black grinned, effortlessly unpinning himself using Biokinesis.
Petyr might not last against the Assassin for long, but he could keep the Servant occupied.
Taking advantage of Zouken's shock, who had gone silent, sensing a greater trap in all this, Black marched up the stairs, reaching Sakura's room.
As he opened the door, the hair on the back of his neck stood up.
On one side, against the wall, and bleeding from the stomach and shoulder, was Shinji Matou, holding terror in his eyes.
On the other side, seated curled up on the bed, was Sakura Matou, her entire figure blurring in and out like a glitch.
And the entire room was filled with black-colored balls that kept bursting with spikes.
Black had never revealed his Mysteries after coming to this timeline, except for the time when he had used Reality Marble.
Now, he buried them even deeper.
Because those Spike Balls were made of Hollow —
— an imaginary element that was highly effective against all Mysteries.
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