Fan Fic / Chaos Theory

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.
— Prologue

Chaos Theory is a Fan Fic 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, among other assorted fics. The plot of this fic deals with the ripple effect of how one seemingly insignificant choice can completely and unrecognizably rewrite fate.

In this story, the proverbial "nail" in question 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:

  • Affably Evil: Avenger is surprisingly polite once summoned. It weirds everyone out because of how far off it was from their expectations of a mindless monter.
  • A God Am I: Dark Sakura claims she will be a goddess when Angra Mainyu is born into the world.
  • Affably Evil: Caster Alter and, later on, Lancer Alter.
  • An Arm and a Leg:
    • Gilgamesh loses his left hand in the battle against Saber, Berserker, and Archer.
    • Lancer Alter cuts off Saber's legs to stop her from being consumed by the Shadow.
    • Archer loses his right arm in the final battle with Gilgamesh. Gilgamesh loses a hand again at almost the same time.
  • And I Must Scream: Caster is turned into a dragon, all that remains of her being part of her torso and her head, silently screaming when the dragon roars.
  • Anti-Hero: Ilya shifts into this at the start of the story—much to her consternation, because Being Good Sucks due to coming with further moral boundaries that she's forced to adhere to for Shirou's sake. The later perks, however, make her less disgruntled about it.
  • Anti-Nihilist: Illya moves into this as time goes on, acknowledging that Humans Are Flawed, and that the world may be screwed up, but that people don't have to be defined by the negative.
  • Arrow Catch: Dark Sakura captures Shirou's Gae Bolg, and tells him that even if it had hit, it wouldn't have worked.
  • Arson, Murder, and Jaywalking: Upon learning that Shirou left the house while sick and hasn't been back for several hours, Fujimura is worried that he "could be passed out in a ditch and die of illness! He could be murdered! He could get me fired."
  • Asshole Victim: It's implied and later explicitly stated that Rin kills Shinji, but the perpetrator and the victim's victim agree that he deserved it.
  • Assimilation Plot: Dark Sakura plans to absorb everyone into Angra Mainyu and send it to the Root.
  • Bait-and-Switch: Ilya opens the front door, expecting her maid and no trouble. However, what the reader knows and she doesn't is that two villains have set out to abduct Ilya. Then:
    "… No fun at all," Ilya muttered, opening the door. "Sella, you took longer to get here than I-"

    And then the attack began, the most dangerous person in Fuyuki striking with sudden, brutal efficiency that broke Shirou's defenses instantly.
...but it was just Taiga, along with the expected maid.
  • Because You Were Nice to Me: This is the fic's turning point from canon: the whole reason Ilya grows fond of Shirou.
    Ilya: Because he was nice to me. He was sweet and kind and treated me like I was special when he didn't have any reason to, and he never asked for anything in return. You'd be surprised how rare that is.
  • Being Good Sucks: Ilya becomes frustrated with how much harder it is to do right rather than easy, to the point of a near-tantrum over it. It pays off some in Chapter 15, but even afterwards she's still quite frustrated.
  • Berserk Button: Three of Gilgamesh's are pressed at once: The Shadow is running around threatening his kingdom, Archer is running around copying his treasures, and his Saber has been tainted by the Shadow. This prompts him to enter the fray when all of the above are fighting at Ryudou Temple.
    • Avenger summoning Enkidu gets him ‘’pissed’’.
  • The Berserker: Berserker, obviously, and Saber Alter at first.
  • Big Bad Ensemble: It's a combination of Kirei Kotomine, Gilgamesh, Zouken Matou & Caster Alter.
  • The Big Bad Shuffle: It starts out with the above Big Bad Ensemble Zouken and Caster Alter being the main antagonists, working together to fulfill their agendas while simultaneously plotting against the other, while Kirei merely observes and Gilgamesh does whatever he wants. However, after Chapter 31, Dark Sakura kills both Zouken and Caster Alter, Kirei becomes The Dragon, and Gilgamesh is reverted to a child after a near-disastrous encounter with Dark Sakura and ends up doing a Heel–Face Turn. Near the end though, Sakura is separated from the Grail's influence, but Kotomine sacrifices himself to incarnate Angra Mainyu as Avenger, whom proceeds to take over as Big Bad.
  • 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. Rider finds this out the hard way.
    • As much as Rin might not want to admit it, she has Sakura's back.
    • In Chapter 22, Shirou goes mental on Caster for hurting—and nearly killing—Ilya after taking her Command Seals.
  • Big "WHAT?!": Taiga's reaction to learning that Ilya is Kiritsugu's daughter.
  • Blade Brake:
    • Lancer Alter does this while fighting Berserker, breaking his arm in the process.
    • Saber does it soon after while fighting Gilgamesh. Saber does it again at the start of her fight with Lancer Alter.
    • Saber Lily does this after using Invisible Air for propulsion while fighting Angra Mainyu's shadow simulacrum of Assassin.
  • Blade Run: Saber Lily uses her opponent's weapon as a ramp to knee him in the face.
  • Blood Knight:
    • Lancer Alter's enthusiasm for a good fight makes his uncorrupted self seem almost calm.
    • Saber Alter is one after Dark Sakura stabilizes her.
    • Saber Lily is one, as well. Her first opponent gets stronger every time she cuts it down and the fate of the world is at stake, but she's happy for the challenging fight.
      Saber Lily: So, the smaller unit can also regenerate. Or is it more like the madness becomes entirely new flesh? What a confounding creature you are. I wonder what it will take to make you stay dead?
      Rider: Are you... enjoying this?
      Saber Lily: [confused] Are you not?
  • Breather Episode:
    • After an intense, multi-sided battle on and around the mountain, the heroes go home to regroup. The next few chapters alternate between humor and sharing information, with bits of drama sprinkled in leading into the next buildup of tension.
    • After an action-packed few chapters wherein things go From Bad to Worse multiple times in one night, the next chapter-and-a-half consists of comedy with a side of fluff as the remaining heroes make preparations for the final battle. Double Subverted; see Bait and Switch above.
  • Butt-Monkey:
    • The author loves tormenting Shinji any chance the opportunity comes.
    • Rin to a lesser extent, especially early on in the story. None of her plans go well, she is a victim of the Fastball Special from her own servant on multiple occasions (see below), and she is constantly being trolled by her enemies and allies alike.
  • Call-Back:
    • Upon meeting Archer again, Gilgamesh refers to a To the Pain promise he made the last time they met and says it's time to get on with it.
    • Gilgamesh losing a hand becomes important later when Kirei offers it to Dark Sakura and she uses it as a catalyst to transport herself to Gilgamesh's location.
  • Came Back Wrong: Enkidu especially is corrupted by Avenger when he summons him, Lancer Medusa and Lancelot.
  • Cannibalism Superpower: True Assassin has access to the abilities of anyone consumed by the Shadow.
  • Casting a Shadow: Anyone controlling the Shadow is using shadow/darkness magic, but especially Dark Sakura, whose control over it is complete. She can make constructs and creatures of shadow.
  • Casual Danger Dialog:
    • Saber casually remarks while deflecting a barrage of arrows that she believes Archer is attacking them.
    • Rin and Archer banter some while dodging a rain of fire attacks.
    • Lancer Alter is talking with Shirou and chuckles while dodging a stray shot from the meteor shower of Babylon.
    • Saber Lily is fighting against Lancelot. It takes every ounce of effort she can possibly put into the battle just to fight evenly with her opponent, but she still banters at him.
  • The Cavalry: Each of the remaining Servants is fighting an opponent summoned by Avenger and at a pivotal moment when they gain or are about to gain the advantage, other fighters show up to save the Servants' respective opponents.
  • Cerebus Syndrome: The first couple of chapters are pretty light-hearted, but there're some dark moments to be found in the story, and increasingly so. It never loses its humor and heartwarming, though.
  • Character Death: Major characters, in order: Fake Assassin, Kuzuki, True Assassin (apparently), Berserker, Zouken, Caster, and Archer.
  • The Chew Toy:
    • Shinji, arguably even more than in Canon.
    • Lancer still can't catch a break, what with his being eaten by the Shadow and turned Alter. Though, the fic does Throw the Dog a Bone several times.
    • Berserker will always die before the route even reaches the climax, and this route is no exception, with him falling under Caster's command thanks to Rule Breaker, and Saber being forced to destroy him in order to save Shirou, Ilya, Rin, and Archer.
  • Close-Call Haircut: Saber loses a few hairs to her opponent's weapon during the climax.
  • Clueless Chick Magnet: Shirou, as usual. He starts out with Sakura, then picks up Ilya and Rin, and then Saber.
  • Cold-Blooded Torture: Kirei does this to Rin, effectively paralyzing her first so she can't fight back.
  • The Corruption: The Shadow does this to Caster and Lancer, rather than devouring them outright as was planned by Zouken. It slowly takes over Saber, as well, after her contact with it.
    • Avenger summons corrupt versions of Enkidu, a young Lancer class alt of Medusa, and Lancelot.
  • Cutlass Between the Teeth: Archer projects Kanshou between his teeth after he loses an arm.
  • Cutting the Knot: The goal is to get into the mountain cave housing the greater Grail. Gilgamesh doesn't have the patience to look for the tunnel entrance and decides to create his own by blasting through the mountain with noble phantasms.
  • Dark Action Girl: Rider. Also, arguably the course for Caster Alter.
  • Deadpan Snarker: Archer has a snarky streak he displays frequently. Rin has one that comes up more toward the end.
  • Defiant Captive: Ilya is kidnapped, but when she wakes up she calmly asserts that the heroes will save her and argues with her captors.
  • Defiled Forever: Gilgamesh feels this way about Saber and goes to extra lengths to kill her in Chapter 29, claiming that allowing the Shadow to touch her core without his permission is an even worse infidelity than taking a lover.
  • Defrosting Ice Queen: Saber and Ilya, in different ways.
  • Despair Event Horizon: Dark Saber, who feels she's so far beyond redemption that she's not even going to try.
  • Deus Sex Machina: Used once, defied twice.
    • Does happen between Caster Alter and Sakura Matou in Chapter 20, within one of the latter's dreamscapes.
    • Defied in favor of Blood Magic in Chapter 34 by Shirou to Ilya and by Rin to Child Gilgamesh, with Shirou considerate of Ilya's feelings (and youthful appearance) and Rin far less respectful towards Child Gilgamesh (the feeling is mutual).
  • Dissonant Serenity: Avenger is incredibly polite, which, given its goal, is off-putting to its opponents. Shirou and Saber note that they were expecting something more monstrous.
  • The Dragon: True Assassin to Zouken Matou, being more powerful than him overall but loyal enough to not backstab him.
  • Dragon-in-Chief / Dragon with an Agenda: Caster Alter is both, to different characters:
    • The former to the Dark Grail, which hasn't enough intelligence beyond its loneliness and hunger.
    • The latter to Zouken Matou, who thinks she is incorrigible but will serve him until he no longer needs her; in reality, she's the one pulling his strings.
  • Drunk on the Dark Side: Servants corrupted by the Shadow most definitely get a kick off the near-unlimited prana it provides. Even Saber isn't immune to its lure.
  • Dude, She's Like, in a Coma!: Ilya does this with Shirou to help him with his mana deprivation caused by Rider. Multiple times.
  • Dying as Yourself: After being fatally wounded by Dark Sakura, Archer projects Rule Breaker and kills himself with it, both preventing the Dark Grail from corrupting him and dying as Emiya Shirou rather than as Archer.
  • The End of the World as We Know It: Avenger is going to wipe out humanity and possibly all life on Earth if it isn't stopped.
  • Enemy Mine:
    • They don't team up, but Saber and Rider halt their fight to deal with Archer, who's trying to snipe them.
    • Notably averted between Shirou and Rin: because Ilya chooses not to attack, the Emiya-Tohsaka alliance doesn't form on the first night and they become rivals.
    • Ilya and Saber secretly align on Shirou's side against the other combatants.
    • An Emiya-Einzbern-Tohsaka alliance is officially established when all parties involved learn about the danger posed by the Holy Grail.
    • Gilgamesh joins the heroes after being betrayed by Kirei in order to seek revenge.
  • Even Evil Has Loved Ones: Caster towards both her Masters. She truly did care for Sakura's well-being.
  • Even Evil Has Standards:
    • Kirei has an internal monologue about this, comparing himself to Zouken:
      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.
    • More conventionally, Gilgamesh reacts this way to Caster Alter (and her "pet" shadow monster, Lancer Alter) in Chapter 11.
    • Though not a case of Evil having standards, Ilyasviel mentally compares Gilgamesh's attitude to that of the Shadow in Chapter 15. Gilgamesh is found... wanting, due to his conceit and smug-superiority coming off as more contemptable than the Shadow's anguished loneliness.
    • Caster Alter feels the same way about Zouken as Kirei does. She may be evil and steal people's souls, but at least she's not so slimy about it.
  • Evil Cannot Comprehend Good: Caster cannot understand why Sakura does not want to take bloody revenge against the people who have made her suffer in her life. Kirei eventually lampshades that neither Zouken nor Caster can understand Sakura and explains why.
  • Evil Versus Evil: Kirei Kotomine, Zouken Makiri, and Caster Alter all have conflicting plans and are therefore against each other. Meanwhile, Lancer Alter just wants to indulge himself in fighting and is perfectly willing to damage the plans of people like Zouken and Caster Alter to get it, even though the latter is supposed to be controlling him and the former is supposed to be controlling the latter.
  • Exploited Immunity: Caster Alter, while controlling Berserker, uses explosive attacks that won't harm him but are intended to hurt his opponent.
  • Explosion Propulsion: Shirou uses Rho Aias to let an explosion propel him and Rin toward their destination and away from the enemies holding them up from reaching it.
  • Face Death with Dignity: Berserker does this.
  • Fastball Special:
    • In Chapter 4, Rider throws Shinji into a thorny bush and, hilariously, Shirou throws him into Rin.
    • Archer throws Rin into a thorny bush in Chapter 10.
    • Saber does the same to Shirou in Chapter 13.
    • In chapter 14 Rin gets chucked by Archer (again) into a pond. At least it's better than a bush.
  • Fighting a Shadow: The body Avenger interacts with the group with is merely an avatar, a physical projection of its true existence.
  • Fighting from the Inside: After Saber Alter becomes coherent, she says the reason she was The Berserker at first is because there was a spark of light inside that refused to go out and she was at war with herself.
  • Five-Bad Band: One gets formed partway through the story:
  • Five Man Band: The good guys steadily team up, and as of Chapter 23 the structure seems to be as follows:
    • The Leader - Rin Tohsaka: the one who formulates the structure of the team and coordinates the others as a whole
    • The Lancer - Ilyasviel von Einsbern, being that she bickers and clashes with Rin's personality
    • Smart Guy - Archer: wisecracking, but also the most experienced of the group and an important strategist
    • Big Guy - Saber: with Berserker's death she's the most powerful physically, and her partial corruption puts her control in doubt
    • The Heart - Shirou: the weakest overall, but he's the glue holding them all together and the most "human" of the group
    • Sixth Ranger - Rider, who is forcibly taken by Rin from Shinji, but aids them because it suits her agenda for now.
  • Flat "What.":
    • The response of Archer, Lancer, and True Assassin to Caster Alter in Chapter 9:
      Lancer: What...
      True Assassin: The...
      Archer: [thinking] ...Hell?
    • Shirou responds this way when Ilya goes from near-crying to cheerfully calling him adorably shy.
    • Given several times during the Breather Episode in response to things Ilya says.
  • For Want of a Nail: The nail in question? Shirou responds to Ilya in their first meeting. The story snowballs from that point.
  • Friendly Enemy: Rider. Even when she takes some of Shirou's prana to ensure Sakura doesn't die, she's very considerate about it.
  • From Bad to Worse:
    • Caster takes Ilya's command seals with Rule Breaker, giving her control of BERSERKER.
    • Archer is exhausted, heavily injured and without an arm from fighting against Gilgamesh, and he still has to fight Saber Alter. As Archer remarks that it couldn't get worse, Dark Sakura appears, having consumed Gilgamesh by use of his previously amputated hand.
  • Glasgow Grin: Assassin gives himself one when he cuts away the stitches holding his mouth shut.
  • Godzilla Threshold: When she realizes just how bad things are with Avenger, Ilya actually encourages Shirou's return to the fight even though he's still healing.
  • Go Out with a Smile: As in canon Heaven's Feel, False Assassin does this when sacrificed to summon True Assassin in order to show contempt for his killer by rejecting an Undignified Death.
  • Greater-Scope Villain: Like in the original visual novel, Angra Mainyu is responsible for the Holy Grail's corruption and it influences the Alter Servants and Dark Sakura. However, this time it actually succeeds in manifesting before the heroes can destroy the Grail and it proceeds to take over as Big Bad.
  • Hero Antagonist: Rin, as Shirou's opponent during this War. However, they come to an agreement due to the bigger enemy that is the Shadow and the Dark Grail.
  • Heroic Resolve: Invoked in Sakura by Medea to prevent the former from sacrificing herself.
  • Heroic Sacrifice: Subverted. Sakura forces Zouken to kill her in order to prevent the black Grail from forming. However, she's Only Mostly Dead and is convinced to cling to life when Medea provokes Heroic Resolve from her.
  • Heroic Safe Mode: Shirou's body is on autopilot while automatically recovering from a normally fatal wound, and starts fighting on instinct when he sees Ilya is captured and has been hurt.
  • High-Speed Missile Dodge: Rider dodges a homing sword-arrow by speeding past it. Unfortunately for her, it's a Super-Persistent Missile.
  • Humans Are Flawed: Ilya comes to this conclusion when healing Dark Saber, believing that although humans all have dark sides and regrets, it's not all there is to them, and they don't have to let their darker aspects define them.
  • Hydra Problem: Rider, and later Dark Saber-turned-Saber Lily, are fighting a shadow monster manifested from the Grail. Being a mass of curses, when a head or appendage is cut off the curses spill out and create new "flesh," leaving it with even more appendages than before.
  • Hypercompetent Sidekick: Archer seriously gives off this vibe at times, since almost every significant win for the good guys is at least partially due to something he's done.
  • I Am the Noun: When Kirei asks Sakura if she wants the Holy Grail, she replies that she is the Holy Grail.
  • I Die Free:
    • Ilya tells Rin that the reason she didn't stop Sakura from leaving on a suicide mission is because for once in her life, Sakura was making her own choice about her life instead of being someone's doll, which Ilya empathizes with.
    • Archer kills himself rather than let Dark Sakura corrupt him.
  • I Hate Past Me: Rider meets a younger version of herself and expresses her hatred for that self.
  • I Never Told You My Name: Rin has been suspicious of Archer knowing more than he should for a while, but the last straw for her is when he calls the Einzbern Master "Ilya" despite her having never told them her given name.
  • I'm a Humanitarian: True Assassin is this as per canon. Sakura's version continues this trend by eating Archer's corpse.
  • Impaled with Extreme Prejudice:
    • Sakura impales every single one of Zouken's worms, destroying them and him completely.
    • Played with when Archer is impaled in his right shoulder with so much force that the weapon goes all the way through, leaving him technically not impaled. Soon after, he impales Gilgamesh through the throat with a sword.
    • Shortly after, Archer impales Dark Sakura through the heart with a sword.
  • In Love with Your Carnage: When Dark Saber starts taking down the mountain, Child Gil starts to understand what Gilgamesh sees in her.
  • In Spite of a Nail: The narrative uses "Heaven's Feel" as a base for the most part — most likely due to Sakura and Ilya's greater prominence in that timeline — so despite many differences and some expanded character roles compared to HF, the storyline plays out like HF with a Spanner in the Works (though some elements are just FSN routes in general): Shirou has some measure of attraction for Sakura; Zouken Matou decides to participate in the fifth Grail War, which leads to True Assassin consuming Fake Assassin; Lancer still has a string of really bad luck, though after he's absorbed he becomes much more competent and independent as Lancer Alter; Berserker is still The Dreaded and a Game-Breaker in the early stages of the story and he dies an antagonist, to show how dangerous the real villains are and because he's too powerful, as well as being under the control of the Dark Grail (in a manner of speaking).
  • In the Back:
    • Gilgamesh attacks Archer from behind while Archer's distracted.
    • Archer runs through Dark Sakura from behind shortly after.
    • Kirei stabs Shirou from behind after Shirou releases Sakura from Angra Mainyu.
  • Ironic Echo Cut:
    • In Chapter 22, Lancer Alter is losing badly to Berserker and doesn't mind at all. Then, the scene cuts to Saber, who is stuck sitting in a tree bleeding out from her severed legs:
      No shame in a death like this.
      There would be great shame, Saber knew, in dying like this.
    • When Ilya is kidnapped and Shirou and Rin are fighting the guards on their way to save her, one of her captors expresses doubt Shirou and Rin will reach them.
      Illyasviel von Einzbern: Shirou and Rin can handle anything you have to throw at them. Wait and see.
      Rin Tohsaka: God, we can't handle this.
    • After Saber solves the hydra problem, she heads into the mountain for the next fight.
      She leaped down the pit into the labyrinth, because one should never waste a shortcut, and prepared for her next battle. Arthur or Arturia, there was always a next battle.
      There was not going to be a next battle, if this continued along the path it was currently heading.
  • It's Personal: Rin goes after Shinji for his implied role in Sakura's abuse at the Matou house.
  • Killing Intent: Servants can project and sense killing intent. Lancer has immunity to projectiles that is based solely on this, able to easily weave and dodge his way through barrages by detecting killing intent.
  • Knight of Cerebus: Caster Alter facilitates the events that make the Holy Grail War much darker and more serious.
  • Ladies and Germs: Hilariously invoked by Archer in Chapter 3 (albeit non-verbally) when preparing to kill Shirou, Shinji, and their Servants:
    Archer: Good-bye, Ladies and Gentlemen. Well... ladies, gentleman, and Shinji. I am the bone of my sword.
  • Locked Out of the Loop: For a long time Shirou has no idea that the sweet little ojou he met in Chapter 1 is a participant in the Holy Grail War. Ilya does her best to keep it that way for as long as possible.
  • Loophole Abuse: Shirou's and Archer's spiritual resonance allows Archer to remember a Japanese style of archery that involves emptying the mind of all thoughts. Because this method eliminates his killing intent, it doesn't trigger Lancer's Protection from Arrows skill.
  • Mêlée à Trois: Between Archer, Gilgamesh, and Saber Alter.
  • Mercy Kill: Rider is prepared to do this to Sakura if she cannot be saved.
  • Mistaken for Pedophile: Shirou in Chapter 23, much to his chagrin. Early on, he was only worried about looking like the time he spent with Ilya was sketchy, but upon finding out that she's actually nineteen years old...
    Shirou Emiya: It means all those innocent things she did! Silly kid stuff! They weren't innocent, Tohsaka! They were... they were... she was... those were dates!
  • Morality Pet: Shirou becomes one for Ilya, much to her chagrin.
  • Motive Rant: Dark Sakura exposits at length about what she's planning to do and why when trying to convince others to join her.
  • Mouth Stitched Shut: Caster Alter sews Assassin's mouth shut when she "rebuilds" him.
  • No-Sell: In order to be purged of the Shadow's influence, Saber has to acknowledge that she's human, darkness and all, and accept the best and worst parts of herself while deciding not to follow her darker impulses. When the Shadow tries to take over her again, she's immune to it because all it does is bring out the darkest side of someone and she's already embraced that side as part of herself.
  • No Social Skills: Ilya is clever, but her isolation and lack of any real friends throughout her life means that she's not very graceful in certain social elements; in Chapter 23, she seems to assume that Shirou knew he was going on dates with her despite thinking she was ten and that even if he didn't realize it, it was perfectly acceptable. Whichever one it was, Saber and Rin ultimately get the wrong impression.
  • Noodle Implements: In Chapter 1 (not counting the prologue), Ilya and Rin vaguely contemplate expressing their anger at the one perceived to be responsible using "power tools" and "a variety of bladed instruments," respectively.
  • Not What It Looks Like: In Chapter 23. When Shirou freaks out about the fact that he was, essentially, going out on dates with Ilya, Rin and Saber mistakenly assume that he knew they were dates and that he's freaking out because he didn't know she was nineteen. Of course, Shirou's inability to connect with people and empathize properly means that he didn't even realize that Ilya considered them dates; he thought that he was in an Intergenerational Friendship and misread Ilya's intentions, which then leads to her digging him in even deeper in an attempt to save him. A long, heated discussion ensues offscreen for twenty-four minutes before the matter is resolved.
  • Offhand Backhand: Saber Lily multiple times swings her weapon and without looking cuts down an appendage or head of the monster she's fighting.
  • Or Was It a Dream?: Caster's attempts to corrupt Sakura via illusions projected into her sleeping mind.
  • Oh, Crap!:
    • When the Shadow first appears, Archer quickly realises that the war he's currently in is not the same one he originally dealt with when he was alive.
    • Anyone during their first encounter with a Shadow-corrupted Servant, even Zouken.
    • Archer and Caster Alter when they see the Gate of Babylon raining death upon them.
    • Ilya when she realizes that Sakura plans to merge everything on Earth with Angra Mainyu and send it into the root, effectively making it God.
    • Rin is horrified when she realizes Kirei is a genuine follower of Dark Sakura and not just working some secret plan.
  • The Ojou: Before he learns her name, this is how Shirou addresses Ilya.
  • Only Mostly Dead: Sakura's Heroic Sacrifice is subverted this way.
  • Other Me Annoys Me: Both the normal Rider and the Lancer Rider summoned as a minion of Avenger rub each other the wrong way.
  • Pinned to the Wall: Archer pins Saber Alter to the ground with as many swords as he can control at once.
  • Poor Communication Kills: Inverted. Shirou, who usually dismisses any weirdness or possible ulterior motive he might notice in Ilya's actions, at one point stops her and makes her confess to him in full what she wants them to do and why, avoiding any dramatic misunderstandings.
  • Post-Kiss Catatonia: Shirou is briefly thrown into this by Ilya's "Shut Up" Kiss.
  • Precision F-Strike:
    • Lancer's is Cut Short when Caster Alter deploys the Shadow to attack him in earnest.
    • Archer gives one when he sees Rin, Shirou, and Ilya are all down and he has to try to fight Berserker without hurting them further.
    • Rin's response to Zouken's demands in Chapter 28 is, "Oh, fuck that."
    • Sakura's response to the suggestion that she and Ilya can't do anything to help in the final battle and have to just watch is, "Well. Fuck that." It's all the more poignant because it's Sakura.
  • Precision-Guided Boomerang: Archer exploits this property of Kanshou and Bakuya in battle, even setting up traps by planting them in the ground.
  • Protectorate: Shirou is this for Ilya, as of Chapter 4.
  • Punctuated! For! Emphasis!: Rider declares her intent to kill Avenger, and when it's brushed aside she repeats herself one word at a time.
    Rider: You. Harmed. Her. And. I'm. Going. To. Destroy. You. Don't question it again.
  • Pure Energy: Dark Sakura can summon semi-solid creatures of pure mana.
  • Rage Breaking Point: Rin reaches this when she comes to understand everything that Sakura went through growing up in the Matou household.
  • "The Reason You Suck" Speech: Shirou (of all people) gives one to Shinji in Chapter 4.
  • Revenge: After Kuzuki's death, this becomes Caster's motive.
  • Running Gag: Servants keep throwing their Masters into bushes and water to get them safely out of the way.
  • Screw the Rules, I Make Them!: Kid Gil says that Gilgamesh never did anything illegal because of this trope.
  • She's Back: Saber, upon being purged of the Shadow's corruption by Ilya, makes a glorious Dynamic Entry into the middle of Rider's fight with the shades of True Assassin and Caster's dragon — as Saber Lily.
  • Shout-Out: Sakura's first dream sequence is a huge one to Baldur's Gate II.
  • "Shut Up" Kiss: Ilya kisses Shirou in order to derail his anguished train of thought over not being able to save everyone from the attack on his neighborhood.
  • Slasher Smile: Gilgamesh sports one of these in Chapter 25. It is unnerving enough to scare Kirei.
    Gilgamesh turned to face him, and Kirei felt a slight twinge of fear for the second time. Gilgamesh was smiling. Widely. Ear to ear, an expression of almost childish happiness, but something in his eyes...
    Gilgamesh: It seems I smile when I'm truly angry.
  • Squick: In-Universe. Rin and Archer have to hold back from physically gagging when they see Ilya kiss Shirou.
  • Stealth Hi/Bye: The effect is somewhat lost because Shirou has come looking for him, but Kirei pulls a Stealth Hi when he somehow appears behind Shirou at the church.
  • Super-Persistent Missile: Archer projects Hrunting, a sword whose concept of "not stopping until it hits its target" is somewhat useful in melee combat but extremely useful when it's used as an arrow, and sends one after Saber and then another after Rider.
  • Superpowered Evil Side: Servants who are absorbed by the Shadow come out tainted by its evil influence and boosted by its infinite mana supply.
  • Sword Plant: Saber tends to stab the ground and use her sword for support when she's exhausted. Archer sometimes plants Kanshou or Bakuya in the ground to set up a trap exploiting their attraction to each other.
  • Take That, Scrappy!: Invoked by the author in regards to Shinji, whom he admits to despising—apparently, making him suffer is a joy for him. Not that anyone really minds.
  • Teeth-Clenched Teamwork: In Chapter 10, between Archer, Lancer and True Assassin.
  • Tempting Fate:
    • Caster Alter declares that there will be no more last-minute rescues to stop her from killing Shirou. Immediately after she says so, Rider breaks down the front wall of the room they're in. Zouken hangs a lampshade.
    • Archer, facing down against Saber Alter after tying with Gilgamesh and severely injured, tells himself that things couldn't get too much worse. Then, Dark Sakura shows up.
  • That Man Is Dead:
    • The fully corrupted Saber sees herself as being a separate person from Arturia and desires to cement this by killing everything that tied the old her to the modern era.
    • Saber Lily claims Avenger's tactic meant to cause mental duress won't work on her because the version of her who would be affected by it is dead and gone.
  • There Was a Door: Dark Sakura says this to Rin when Rin and Shirou break through a wall to enter the villains' lair.
  • This Is Gonna Suck: Lancer says it, word-for-word, in Chapter 10.
  • To the Pain: Gilgamesh graphically describes how he will torture Archer as punishment for copying his treasures and says that's only the beginning.
  • Tranquil Fury:
    • Archer manages to anger Gilgamesh to the extent that the latter goes from roaring in rage to speaking softly while promising to inflict untold torments on Archer.
    • Archer quietly and calmly resolves to torture Caster Alter to death upon seeing Ilya being held hostage and the fear and pain she's in.
  • Undying Loyalty: Rider to Sakura, as per canon. Also, Caster Alter to Sakura.
  • Utopia Justifies the Means: Dark Sakura believes she's going to create a utopia, even if it means assimilating everyone into Angra Mainyu and heading to the Root.
  • Villainous Breakdown: Dark Sakura initially is in control of Angra Mainyu's influence over her and is still calm and kind even while working toward an evil goal, but she loses control when Shirou manages to activate his own version of Unlimited Blade Works and becomes a mindless rage machine.
  • Voodoo Zombie: When Servants die to the Shadow, its controller can call them back out to serve him or her.
  • We Can Rule Together: Dark Sakura tries to convince the heroes and the corrupted Saber to join her side. They all refuse, with Saber Alter outright declaring her intent to kill her.
  • Well-Intentioned Extremist:
    • Dark Sakura seems to believe her actions to be in humanity's best interest.
    • Avenger considers itself an ally of humanity. It intends to wipe out humanity in order to fulfill their collective wish for a greater power to be the cause of their suffering.
  • Wham Episode:
    • Chapter 8.
    • Chapter 21 tops it. Caster Alter now has control over Berserker after using Rule Breaker on Ilya, Saber is missing her legs, and Shirou had a hole blown through his chest.
    • Chapter 22: Rider nearly dies fighting Berserker, she teams up with Assassin and Lancer Alter to stop him... and Lancer Alter kills Assassin in revenge for an earlier slight. Shirou draws on incredible power to protect the now-defenseless Ilya from Caster Alter and injures her. Saber is able to pull beyond her reserves and destroy Berserker to protect Shirou, Ilya and Rin... but only because she somehow drew on some of the Tainted Grail's power. And Caster Alter is smiling at this last bit.
    • Chapter 27: Zouken has Caster's minions kill everyone in Shirou's neighborhood and then set their houses alight, unleashing Caster Alter to distract Saber and Lancer Alter to deal with Archer, and then tells Shirou this is his idea of a peaceful negotiation. If he doesn't hand over Ilya in four hours and have the Servants feed themselves to the Grail, he'll recreate the Fuyuki fire on a larger scale.
    • Chapter 31: Caster ends up converting Sakura to her Dark state to save her life, only for Dark Sakura to absorb her and Zouken and decide to work with Kotomine to birth a dark god.
  • Wild Card: All of the corrupted Servants have their own agendas and are perfectly happy to mess up the plans of their "masters" to get them.
    • Caster Alter wants Sakura to embrace her inner darkness and in doing so get revenge on everyone who has wronged her.
    • Lancer Alter wants to fight and kill until either he's dead or everyone else is, and is perfectly happy to screw up Caster and Zouken's plans in order to get the war he craves.
    • Saber Alter wants to take revenge against the system which she wasted her life on and become a new person; i.e., she wants to destroy the Holy Grail and everything and everyone associated with it. This includes Dark Sakura, whom she regards as another enemy.
  • Won't Take "Yes" for an Answer: Downplayed. Shirou expects to have to fight Ilya tooth and nail over him rejoining the fight. As he's gearing up for the argument:
    Illyasviel von Einzbern: You're going to have to go back into the mountain.
    Shirou Emiya: Ilya, I'm going to... wait, what?
  • Woobie, Destroyer of Worlds: Dark Saber and Dark Sakura. Ilya considers it a better result than someone more malicious getting the Dark Grail's power.
  • "World of Cardboard" Speech:
    • Ilya gives an internal monologue to this effect in Chapter 4, regarding Shirou.
    • Also, Lancer Alter in Chapter 13.
      Lancer Alter: 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. The Hound of Chulann... 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!
    • Ilya does this later to Dark Saber, pointing out that her rampage is illogical and petty.
  • Worthy Opponent: Gilgamesh decides that contrary to his first impression of her, the corrupted Saber is a worthy opponent deserving of his full power.
  • Wronski Feint: Rider passes over Saber to put her in-between Rider and the sword-arrow chasing her.