Chaos Theory (fanfic)

"But mostly? The assorted plans at play here would be going very, very wrong due to the actions of a no-name, no-count, utterly talentless Magus by the name of Shirou Emiya. He had no magic worth mentioning, no combat experience of note, and no plan for or knowledge of the War he was about to enter. He did, however, have one trait that had derailed a countless number of such grand, far-reaching schemes throughout history."

"You see, he really, really wanted to be a hero."

- "Chaos Theory" - the final lines of the story's Prologue

Chaos Theory is a Fanfic in the Fate/stay night branch of the Nasuverse. Posted on Fanfiction.Net by the Moczo siblings - who wrote Manchester Lost, Uninvited Guests and Infinity - it is a For Want of a Nail fanfic which deals with the ripple effect of how one seemingly insignificant choice can rewrite the fates of multiple individuals.

In this story, the change comes when Shirou Emiya first meets Ilyasviel von Einzbern, who in Canon delivers her warning to him about summoning a Servant before departing. Here, however:

"Shirou stopped, and watched the girl stroll past. She… something about her just said 'do not follow me' to his mind. Like he was risking his life by approaching her. But…"

"Sometimes, it's the tiniest little things that can change the world."

"Shirou sprinted after the departing girl, shouting, "Wait, wait up a second!""

"The girl, her eyes wide with more shock than should probably have been in them, turned to face him. "Um... huh?" She said, eloquently."

"Shirou knelt down so that he could look her in the eyes, and put on his warmest smile. Her clothes looked very well made, so best to assume she had money and behave with proper respect; though really, he would have anyway. Even if she wasn't actually upper-class, it was the rare little girl who wouldn't get a small thrill out of being talked to like she was a Lady. "Hello, ojou-chan. Are you all alone?""

Having believed Shirou to be - like Kiritsugu Emiya - a heartless person, this act of kindness throws Ilya off her game. In addition to that, the effects of this meeting - though small at first - steadily propel the Holy Grail War into a never-before-seen direction, where friends might become foes, the people you trust are keeping secrets from you, and villains with far-reaching schemes find their plans derailed - and in some cases, enhanced - by simple chance.

In the middle of all this chaos are two souls fighting for survival. Caught in a conflict he never saw coming (and this time without Rin Tohsaka as his guide and ally), Shirou must - along with Saber - find some purchase in a conflict that could destroy everything he cares about. Meanwhile Ilya - who grows closer to Shirou than she ever thought possible - must face her past and her inner demons as she fights a War that will not only test her most fundamental beliefs, but just might prove to be her much-needed salvation.

This story - considered by some fans to be a Fanon interpretation of the never-made "Ilya Route", takes many elements from the Heaven's Feel route while nonetheless telling its own unique tale. Started in 2010, it combines the Moczo-brand style of humour (Uninvited Guests & Manchester Lost) with their other strengths of superb plotting, characterisation and story-telling (Infinity), to create a worthwhile reading experience.

This story comes with very positive recommendations on TV Tropes.

Chaos Theory contains examples of:
"But at the very least, even on those rare occasions that his conscience (yes, despite what anyone else might say, he did have one) flared up, he could always say 'At least I'm not Zouken'. The elderly Magus disgusted him, repelled him in every way and on every level. Kirei was, after all, completely selfless in his own way. His means of doing so was bizarre, perhaps, but he cared only for other people."
 * Affably Evil:.
 * Anti-Hero: Ilya is a Type III.
 * Anti-Villain: Rin, as Shirou's opponent during this War, is essentially a Hero Antagonist.
 * Because You Were Nice to Me: Not stated yet, but this is why Ilya grows fond of Shirou.
 * Big Sister Instinct: If you don't want Ilya to sic Berserker on you, then do not harm a single hair on Shirou's head. found this out the hard way.
 * As much as Rin might not want to admit it, she has Sakura's back.
 * Blood Knight:
 * Cerebus Syndrome: The first couple of Chapters are pretty damn light-hearted, but there's some dark moments to be found in the story, and increasingly so. It never totally loses it's humour and heartwarming, though.
 * The Chew Toy: Shinji, arguably even more than in Canon.
 * Dark Action Girl: Rider, of course. Also, arguably the course for.
 * Dude, She's Like, in a Coma: does this with Shirou to help him with his mana deprivation caused by . Multiple times.
 * Enemy Mine: Notably averted between Shirou and Rin - because, the Emiya-Tohsaka alliance hasn't formed yet (and so far, there's no indication that it even will).
 * Even Evil Has Standards: Kirei has an internal monologue about this, comparing himself to Zouken:

"Lancer: What...
 * More conventionally, Gilgamesh reacts this way to in Chapter 12.
 * Evil Versus Evil: Kirei Kotomine vs. Zouken Makiri vs..
 * Fastball Special: Hilariously, Shirou does this to Shinji in Chapter 4.
 * And then Archer does it to Rin in chapter 10.
 * And then Shirou gets in on the action courtesy of Saber in chapter 14.
 * In chapter 15 Rin gets chucked by Archer (again) into a pond. At least it's better than a bush.
 * Flat What: The response of Archer, Lancer, and True Assassin to in Chapter 9:

True Assassin: The...

Archer (thinking): ...Hell?"

"Shinji: "H-how... how dare..."
 * For Want of a Nail
 * Freak-Out: Archer goes into borderline hysterics when he realises that on the Holy Grail War's first night.
 * Friendly Enemy: Rider, of course. Even when, she's very considerate about it.
 * Heel Realisation: Ilya's is a slow-burning one, but it's coming.
 * Knight of Cerebus:.
 * Locked Out of the Loop: Shirou doesn't yet know that the sweet little ojou he met in Chapter 1 is a participant of the Holy Grail War.
 * Morality Pet: Though he doesn't yet know it, Shirou is quickly becoming one for Ilya.
 * Or Was It a Dream??: Caster's
 * Oh Crap: After the Freak-Out mentioned above, Archer quickly realises that the War he's currently in is not the same one he'd originally dealt with when.
 * Pretty much anyone during their first encounter with Even Zouken!
 * The Ojou: Before he learns her name, this is how Shirou addresses Ilya.
 * Protectorate: Shirou is this for Ilya, as of Chapter 4.
 * "The Reason You Suck" Speech: Shirou (of all people) gives one to Shinji in Chapter 4.
 * Revenge: After, this becomes motive.
 * Shout-Out: Sakura's first dream sequence is a HUGE one to Baldur's Gate II.
 * Shut UP, Hannibal: After Shirou's "The Reason You Suck" Speech to Shinji (above):
 * Shut UP, Hannibal: After Shirou's "The Reason You Suck" Speech to Shinji (above):

Shirou: "I was completely serious about beating you unconscious, Shinji."

Shinji stopped talking."

":"Fallen? Saber… you know who I am. I spent my entire life desiring battle. Glory. And I spent each and every bit of it as someone's damn lapdog. but oooooh, things are different now! My new Master runs only on instinct. It has no goals, it's just a monster that wants to feed, to hunt and kill the Seven Servants. To face down each one, defeat them, and devour them." ... "That's all it wants to do, and all it wants me to do. And I can do it however I want, with my so-called Master too mindless to do anything about it but follow me in a frenzy, begging for scraps. I don't have anyone holding me back, Saber. Nobody's leash stopping me from claiming the ultimate battle that I always wanted. Fallen? For the first time in my life, I'm free!""
 * Super-Powered Evil Side:.
 * Teeth-Clenched Teamwork: In Chapter 10, between.
 * This Is Gonna Suck: Lancer says it, word-for-word, in Chapter 10.
 * Took a Level In Badass:, and how!
 * Undying Loyalty: Rider to Sakura, as per canon.
 * Wham Chapter:.
 * "World of Cardboard" Internal Monologue: Ilya in Chapter 4, regarding Shirou.
 * Also, in Chapter 13.