The Forgotten Promise [Illya Side Story]

A promise that was forgotten

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⚠️Spoiler Warning⚠️
This side story contains spoilers from the main story of Treacherous Knight and her Master. To avoid any spoilers or confusion it is highly recommended that you read from the main chapters of the story otherwise...
You...Have...Been...WARNED!
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"I so enjoy watching history warp as words pass from the lips of one to the ears of another. Imperfectly formed, half understood, poorly remembered."

-Outsider

Present time
POV: Y/N

Y/N: "Out into the world once more...How ironic that the coming war would be here...In this god forsaken city. I never thought I'd be back here again perhaps it is fate that I'd return to this city where I was born and raised in by her...for a short while anyway...Just trying to remember her was difficult...How far will I go to exact my revenge...? What will I have to become to win the war?"
???: "Talking to yourself again or perhaps the black eyed man who speaks to you in the shadows?"
Y/N: "Just feeling nostalgic is all."
???: "Whats there to feel nostalgic about? This city has had nothing but its fare share of dark history dating back to a plague epidemic to an Empress being assassinate. Who do you think would want to remember that?"
Y/N: "I once believed that the world was a kind and gentle place."
???: "And now?"
Y/N: "I was a fool to think such things but despite the cruelty the world holds it is not without its beauty. This city may have had its fair share of dark memories behind it but despite that it has come along way since then."
???: "Hmph, perhaps...But that is not what I'm here for."
Y/N: "What are you here for?"
???: "Tell me about the Einzbern girl tell me about the Emiya family."
Y/N: "I've already told you about my time In Fuyuki with the Emiya family."
???: "Yes but there was more to that story then you  were letting on about."
Y/N: "Perceptive as always I see very well I'll tell you the rest."

Forgotten Promise
POV: Y/N

I was on a operating table in a secluded place far from any prying eyes could see. Kiritsugu was there aiding me in the creation of a mystic code involving origin rounds.

Kiritsugu: "I'll ask you one more time...are you sure you want to go through with this?"
Y/N: "Yes...I'm sure."
Kiritsugu: "You understand that you could die from this procedure?"
Y/N: "I understand the risks but I'm going to need an ace in the hole for the war to come and origin rounds just so happens to be that ace."
Kiritsugu: "Just so you know this will not be pleasant for you."
Y/N: "I've endured worst Please start the procedure..."
Kiritsugu: "The human soul can only take so much before it's sprit eventually breaks."