Day 6: Zouken — Hollow Assassin
Lying on a bed in the apartment he had rented as a temporary base, Zouken Matou probed at a sore spot on his side. A nagging pain was developing there, a new addition to the chorus of chronic aches and twinges that plagued his decaying body. In this spot, a patch of skin which had been unblemished mere days before had now turned black and split like an overripe fruit, exposing the stinking worm-ridden carrion beneath. Zouken gave a minor grunt of irritation as he ordered the worms to repair his appearance by consuming and replacing the rotted flesh. He had switched bodies and filled up on prana in preparation for the War, hoping to stay in good condition for the duration, but supplying prana to both True Rider and False Assassin at the same time was taking a greater toll on his body than he'd anticipated. Just as well that Shinji, bumbling fool that he was, hadn't somehow managed to convince the False Rider to make a contract with him; even provided a limitless supply of victims, his Crest Worms couldn't devour souls fast enough to produce enough prana for three Servants at once.
Now that Shinji had unsurprisingly gotten himself killed, Zouken was considering shutting of the flow of prana to True Rider. It was not a particularly powerful Servant, nor was it likely to ever pledge loyalty to a Matou again after enduring Shinji as its Master. Furthermore, False Assassin was an infinitely superior tool for Zouken's purposes. But, on the other hand, there was still some potential value in using True Rider as a scout or a decoy against the other Masters, and the latent soul-consuming bounded field it had erected over the school that Tohsaka and Emiya attended could also prove useful in the future. Zouken did not needlessly discard resources which had not yet been fully exploited, and decided to wait and see what True Rider did next before coming to a decision. Currently, it seemed to be heading in the same general direction as the Matou family house. Returning to the location of its summoning, perhaps?
Zouken couldn't think of any reason why it might want to go back to his house, but his dilemma would quickly resolve itself if it did. Though his worms retained a vigilant watch over the perimeter of the grounds and the upper stories of the house, the basement was a gap in his perception, a well of utter darkness from which nothing returned. The cause was obvious: the Shadow leaking from the polluted Grail within Sakura was hungry for prana, and was reaching out and devouring the souls of anything within its reach. The Crest Worms that Zouken had left in the pit had been the most immediate targets, but there was no way their meager lives could sate the ravenous hunger of the Grail; it likely wouldn't be long before Sakura left the house and began hunting for more. Woe betide any Servant which crossed paths with the Shadow: however great their stature as Heroic Spirits, they had been summoned by the ritual specifically so that their souls could become fuel for the Grail, and could no more fight it than gasoline could fight a flame.
Still, the majority of the Shadow's victims would likely be humans; though their souls were so much weaker than those of Servants, they were also far more numerous, and far less likely to recognize the danger. The people of Fuyuki city thought they knew fear because of the False Berserker killing at random, but that sad creature's few victims would soon be forgotten when the Shadow began to feast in earnest. It would not carefully select its victims, like the False Berserker was based on whatever madness plagued it, but would become a dark flood extinguishing all light in its path. Not that Zouken himself needed fear the Shadow, of course. After he gained his wish from the uncorrupted Grail, he would break the Shadow's vessel and prevent it from being born, just as Kiritsugu had done in the previous War. Fuyuki city would burn again, as cursed mud spilled like blood from a sundered womb; but having attained his wish, there would be no longer be any reason for Zouken to leave the ritual in place. He would break the very foundations of the Heaven's Feel, ending the Holy Grail War for all time: never again would the Cup of Heaven descend upon Fuyuki with the promise of miracles. The centuries-long dreams of the Einzberns and Tohsakas would be shattered, but Zouken cared only that his ancient wish be granted — to hell with the wishes of the others.
In the short term, things were a bit trickier. Zouken did not want to break the vessel until after his wish had been granted, lest the spilling pollution and curses contaminate the White Grail he had gone through so much effort to call to this world with the Second True Magic, Kaleidoscope. The Shadow would attack him just as eagerly as anyone else if he crossed paths with it, so it would be best for him to avoid it entirely. As such, he had placed a special Crest Worm in Sakura's chest, bonded to one of the nerves on her heart. This worm was currently dormant, tied to Sakura's own prana rather than emitting prana of its own, so the Shadow couldn't detect it. By tracking the worm's location, he could always know where Sakura was, and therefore the Shadow as well.
Zouken was jolted from his reverie by the sound of one of the room's windows being opened. He opened his eyes to see False Assassin pushing open the window while staring outside with unusual intensity. It raised its left arm, which glowed faintly as it built up prana; then a ghostly hand and arm stretched out from the Servant's limb and extended out the window.
"And just what are you doing, Assassin?" Zouken asked irritably.
Instead of responding, False Assassin retracted its spiritual arm. Clutched tightly in its spectral fingers was a somewhat confused-looking pigeon. Without a moment's hesitation, the Servant swung down the knife clutched in its other hand and stabbed the bird, impaling it before it could even notice it was being attacked. Surprisingly, there was no blood on the knife when False Assassin pulled it out. The pigeon was enveloped by a silent blue flame and faded away, leaving no trace. It had not been a real bird, then, but a magical construct; a familiar sent by some other Master to spy on Zouken.
"Commendably well spotted." Zouken said. "However, rather than immediately destroying it, it would have been more beneficial to analyze its magic energy to determine who created it."
"I don't know how to analyze magic like that." the False Assassin said. "All I know how to do is kill. I told you such when we made our pact:"
It had, Zouken recalled. It had stated that it did not know how to come up with strategies or tactics for winning the War, did not know how to protect him as a bodyguard, did not know how to go on scouting or reconnaissance missions, and knew naught of identifying magecraft. It could do one thing only: it could kill. But that one thing it could do, it could do more effectively than any other Servant in the War. False Assassin was a highly specialized tool, effective only in narrow circumstances — but a powerful enough of a tool that it was all Zouken would need to win the War.
"Hmmph." Zouken grunted, conceding the point. "I doubt any of the children have the skill — except perhaps the Einzbern doll. It could be that wretch Kotomine trying to keep tabs on me, of course. And there's the False Caster running around as well — it's hard to know exactly what it's capable of, given that it was summoned from a completely different world. Ah, the greater one's ambitions, the more fools who stand in one's way; isn't that right, Assassin?"
"Which world am I from?" False Assassin asked. "Or rather, which Grail?"
"What's this, now?" Zouken asked.
"I've been thinking about what you said." False Assassin said. "This is a War involving two Grails: one True, and one False; one tainted, and one pure. Which was I summoned from?"
"When a magus peforms a summoning, he calls forth and forms a contract with a Servant from the original, corrupted Grail — the Black Grail whose vessel is within Sakura. As a side-effect, a Servant is called forth from the false but pure Grail — the White Grail whose vessel is within Ilyasviel. Since you appeared without any contract after the other Assassin was summoned, it is clear that you were called by the White Grail. Thus, you are False Assassin."
"I see." False Assassin said listlessly.
"Not the answer you were hoping for?" Zouken asked.
"Ever since being summoned, I've been troubled by a sense of wrongness." False Assassin said. "This painful emptiness, this unquenchable bloodlust. If I had been summoned from the tainted Grail, then its corruption could be to blame for my condition. But if I am from the pure Grail, then this is my essential nature as a Heroic Spirit. I'm nothing but a homicidal maniac, an empty shell which can revel only in slaughter."
"Oh, is that all?" Zouken said. "Some vague existential angst? You're just like that fool Kotomine, getting all torn up over some imagined conflict between your lofty morals and your base nature. It's pointless to worry about such things. Instead of agonizing over your nature, you should focus on the task at hand. Assist me in winning the Holy Grail, and you will gain a wish for yourself as well."
Not that Zouken would allow False Assassin to wish on the Grail, of course. He didn't trust such power in the hands of anyone other than himself. The moment he won the War, he would use a Command Spell to order the Servant to stab its own heart. But the Servant wasn't likely to cooperate if it knew this; and if the prospect of a wish could get it past whatever emotional hangups were making it act so nihilistically apathetic, Zouken would dangle that bait.
"Wish?" False Assassin asked. "I have no wish, no desires. If ever I did, they were lost when I became a Servant."
"That sounds more like a failure of imagination than anything else." Zouken said. "You were just complaining about feeling broken. As an omnipotent device capable of granting any wish, the Grail could easily fix you. If you want to be a normal human with mundane human desires, ask the Grail to remove your compulsion to kill. Or, if you prefer to live as a monster, ask the Grail to remove your human conscience so that you may take pleasure in indulging your darkest urges."
The False Assassin seemed to consider it for a moment, then shook its head.
"No, that wouldn't work." it said. "I have an emotional desire to kill and a moral desire to not kill; but other than that, there is nothing but void inside of me. If I were to wish away my bloodlust, nothing would remain of me but an empty shell in the shape of a girl. Likewise, the guilt I feel over my desire to kill is my sole remaining emotion; if I were to wish that away, there would be nothing human left of me, just a mindless hateful void. I think... my Origin must be Void. And no matter the Grail's power, it cannot change this; just as any number multiplied by zero yields zero, any wish applied to my nature will yield Void."
"Then, simply ask the Grail for contentment, the ability to accept your present condition rather than futilely longing to change it." Zouken suggested. "There's nothing wrong with living outside the boundaries of what ordinary humans deem acceptable. I care not if they call me abomination, because I have a great purpose they cannot imagine. What cares the butcher for the opinion of the chattel?"
The False Assassin turned and gazed unwaveringly at him with its dark, empty eyes.
"Don't get the wrong idea." it said. "I feel guilty about killing humans, but I'd be just fine killing a monster like you."
"Kihihihihihi!" Zouken gave a rasping laugh. "Did I offend that bothersome conscience of yours? Well, you might be a self-admitted homicidal maniac, but I have not the slightest fear at dying by your knife, False Assassin. Oh, you could certainly destroy this sad, half-rotten husk I'm currently wearing, but it wouldn't actually harm me. My actual soul is hidden somewhere quite safe, someplace you'll never be able to find."
He flashed the Servant a wide, rotten-toothed grin, and it turned its head away in disgust.
"But if you're looking for an opportunity to kill with a clear conscience, rest assured: your time will soon come." Zouken continued. "With two Grails, Fuyuki is practically teeming with Servants — and with one of the Grails polluted, some are no doubt twisted abominations that not even a saint would be able to forgive."