By the time Kaelith arrived in Fuyuki City, it was already approaching dusk.
"That'll be 14,700 yen," the taxi driver said, looking back at him through the rearview mirror.
"Alright. Just a moment."
Only in Japan could a taxi ride cost more than an escort service. Kaelith clicked his tongue internally as he pulled two large bills from his wallet.
"Thank you very much. Have a pleasant evening."
Stepping out through the automatically opening door, Kaelith walked under the orange glow of sunset toward a gloomy, lifeless mansion.
This was none other than the legendary pilgrimage site for every Fate-world isekai traveler: the Matou residence.
You could skip the Clock Tower, you could avoid Chaldea, but if you were a Type-Moon transmigrant, you absolutely could not skip the Matou house.
Before the gate of the insect-filled Matou manor stood an old man who looked like a mummified corpse.
Sunken eye sockets glinted with a sharp gaze, and his small, withered body radiated a disproportionate pressure.
"Long time no see, Kaelith."
"Yo, Makiri." Kaelith waved lazily. "Glad to see you're still so spry. Nothing makes me happier."
The old man's name was Matou Zouken, lord of this estate and head of the Matou family, one of Fuyuki's three founding families of the Holy Grail War.
He was one of the creators of the Grail War and the inventor of the Command Seal system.
Once, Makiri Zouken had been a formidable magus, but now he was nothing more than a grotesque monster sustained by five centuries of drinking human blood.
Unable to stand in sunlight, he was a literal non-human creature.
After a brief exchange at the door, Kaelith was soon walking the eerie corridors of the Matou manor and sitting on a couch in the reception room.
"I've obtained my qualification."
Kaelith raised his right hand, displaying the three crimson seals that had appeared on the back of it two hours earlier when he entered Fuyuki's territory.
"Oh? Now that is… a fascinating pattern. It seems this Holy Grail War is worth getting excited for. But Kaelith, you didn't come all this way just to report that, did you?"
"As expected of you, Makiri . No. I'm here to say my final goodbyes to Sakura."
Zouken's murky eyes narrowed.
"Meaning?"
"Meaning, as per our agreement… tonight, you will plant a Crest Worm into Sakura's body." Kaelith's voice was light, almost casual.
Zouken's frail body trembled faintly. A cruel smile crept onto his lips.
"Hmph. I knew I didn't misjudge you. You truly are an amusing man."
"Haha… same to you."
In the dim room, the handsome youth and the hideous old monster locked eyes, both wearing chillingly wicked smiles.
Sunset filtered through the curtains and illuminated Zouken's face, sending his thoughts drifting back to the day they met.
…
A year ago, not long after the Matou family took in the second daughter of the Tohsaka household.
The moment Zouken first saw Kaelith, the five-century-old monster felt as if his internal sense of time simply stopped.
The boy's short, slender frame emanated a presence far too overwhelming for his build.
On a face beautiful enough to seem inhuman, he wore a smile that didn't reach his eyes.
But most suffocating of all were Kaelith's pitch-black, icy pupils.
Simply meeting those eyes made the ancient magus feel like he was being pulled into a black hole at absolute zero.
What sort of monster had appeared before him?
That was his first thought.
"I'm a demon."
The boy introduced himself, and Zouken accepted it instantly.
Zouken was a worm who degraded himself by consuming human lives. Kaelith was a demon who evolved by consuming souls.
Their scale of existence differed, their natures diverged entirely, but they shared one undeniable trait:
Beneath their human skins lay pure, unfiltered malice.
A year ago, Kaelith approached Zouken and proposed a deal.
"I'll fight in the Fourth Holy Grail War on behalf of the Matou family. In return, you will postpone implanting Crest Worms into Sakura for one year. During that year, you won't touch her, and I'll drop by now and then to play with her. Don't worry, I'm not interested in that girl. She's still Matou property. When the year ends, the Tohsaka girl is yours to do with as you like."
"What is your goal?"
Unable to comprehend, Zouken asked instinctively.
"I just want to get along with the Tohsaka girl," Kaelith said with a cold smile.
"…Before she's broken by the worms."
"...!!!"
Realization struck the old magus like lightning, and his eyes widened.
The boy before him was a monster beyond his imagination.
Kaelith intended to build trust with Sakura, lift her up, make her rely on him completely…
Then betray her in the most absolute, devastating way.
To raise an innocent girl to the heaven, only to smash her into the ground.
One could easily imagine the despair, hatred, agony, and sorrow Sakura would feel.
Staring into Kaelith's black eyes, Zouken felt genuine terror.
This boy fed on human suffering and savored it.
The pact was sealed.
Magus and demon forged a contract.
Zouken would protect Sakura's safety and daily life for one year until the day Kaelith decided to "enjoy" her.
In exchange, Kaelith would participate in the Fourth Holy Grail War as a Matou and, if victorious, hand the Grail over without condition.
Naturally, the contract included clauses ensuring neither party could harm the other.
This was the man who created Command Seals.
In terms of contracts and binding magecraft, Matou Zouken was unparalleled.
No matter how powerful Kaelith was, he couldn't violate the pact, just as Servants cannot disobey Command Seals.
Zouken was pleased with this risk-free bargain, and he developed a grudging admiration for Kaelith.
Over the following year, Kaelith traveled back and forth between Tokyo and Fuyuki every three weeks.
Each visit, he brought Sakura expensive gifts and souvenirs one could only buy in the capital, all to make the girl smile.
The Matou manor was gloomy and cold, a terrible environment for a child.
Naturally, Kaelith broke down her defenses and became her emotional support.
Sakura shyly called him "big brother," opened her heart, and smiled for him.
Perhaps because she was separated from her overly capable sister, she even became more outgoing than when she lived with the Tohsakas.
Zouken saw all of it, and reveled in it.
"Hehehe… so this is what they call 'whom the gods wish to destroy, they first drive mad.'"
And so, the year came to an end.
Half a month early, Kaelith informed Zouken to prepare the worms in the pit.
Two demons wearing human faces were about to prepare a grand, bloody ritual for a girl living in a dream.
Tonight was the night.