These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Alternate Character Interpretation: Kirei provices an interesting case. We already know he enjoys the suffering of others, but it is unclear whether or not that is his greatest wish. While Angry Mainyu creates slaughter for him and he believes this to be his realization, one should not forget that the Grail interprets any wish in the most murderous way possible. Kirei's subconscious desire might have been something else entirely.
Base Breaker: The anime is almost universally praised by the average viewers. However, among bloggers, the opinion is more or less split, mostly due to the heavy Info Dump nature of the work.
Kiritsugu is a quite controversial character among the fandom.
Tokiomi Tohsaka. His perceived blandness (actually referenced in-universe as the reason Gilgamesh hates him!) and the wild popularity of his Arch-Enemy Kariya might have something to do with it. Not to mention the controversy regarding Tokiomi's decision to give Sakura to the Matou family, causing the girl years of physical torment. But it seems that he didn't know what would happen to Sakura and truly thought it'd keep her from losing her magical potential due to family rules, had quite a few Pet the Dog moments with his family and genuinely trusted his disciple Kotomine, only to be stabbed in the back by him.
Episode 24 of the anime, for cutting out important aspects of Berserker's behavior and his fight with Saber, as well as altering Kariya's final scene in a way which made Sakura seem considerably more insensitive to him. Mainly splits along your opinion of his overall importance to the plot and Saber's character.
Double Standard: Sola-Ui's actions of being a Stalker with a Crush towards Lancer and coercing Kayneth into giving her the Command Spells earn her a lot of hatred and titles such as "whore" and "slut", and while not harmless they're incredibly tame compared to those of many other male characters, such as Gilgamesh, Caster and Ryuunosuke, and Kirei, all of whom get little to no flack over their own actions and are very quick to be shrugged off. Having a vagina is apparently a worse sin than being a Complete Monster or a Jerk Ass, it seems. Although her lack of charisma or other notable characteristics that the former possess may also play a role in it as well.
Especially considering her actions aren't fully her fault, but due to a curse on Lancer that did not mix well with poor Sola-Ui's already present emotions and frustrations, although she could have resisted the curse initially if she had tried. (Ky is, initially). Should've read up on the mythology of your hero there, Kayneth, and not summon a dude who's cursed into making women desperately fall in love with him without him even wanting to.
That's not Kayneth's fault, either. If Waver hadn't taken the item needed to summon Alexander, he would have had Rider as a Servant in the first place. It's likely Kayneth only summoned Lancer as a last-minute resort.
Gilgamesh, unsurprising since this also applies to his original incarnation. Perhaps Justified as Gen Urobuchi has stated in an interview that his favorite characters are Gilgamesh and Kirei.
Disturbingly Caster and Uryuu also get some of this, with some labeling them Yanderes. Caster at least show a bit of a human side while talking about his old companion Jeanne D'arc, but Uryuu has no such soft spots, and the closest he gets to a dere side is with Caster, who he appreciates mostly because they're equally depraved.
The most recent TYPE-MOON populatity poll clocked Rider as the second most popular male character in the Nasuverse (being beaten only by longtime fan-favorite Archer) and the sixth most popular character overall, leaving other Ensemble Darkhorses of the franchise (such as Cu Chulainn, Kotomine, and even Gilgamesh himself) in the dust. For a character that Nasu admits is more of Urobuchi's creation than his, it's quite impressive.
Kayneth has also received an unexpected fandom from /a/. And Pixiv.
Kariya is absolutely adored in both Japan and the West. But especially Japan.
Ryuunosuke is impressively popular for a homicidal sadist. Apparently, he is loved by the female staff members of Ufotable.
Probably the best example of this, however, would be Kirei's wife Claudia Ortensia, whose actual appearance in Fate/stay night lasts less then a minute, the only reason we know what she looks like is a miniscule appearance in Character Materials and so little is known about her that for a long time she didn't even have a name. With the airing of the anime, Kirei's new fanbase on Pixiv has taken quite a liking to Claudia; fanart of her with Kirei is common and they have become a mildly popular ship, but she also gets surprising amounts of fanart depicting her alone, though her design probably helped with the latter.
Evil Is Cool: Gilgamesh and Kirei are some of the most popular characters in the entire franchise.
Foe Yay: Kiritsugu and Kotomine, Saber and Lancer.
Fridge Brilliance: Iskander's death scene mirrors his life as explained in the flashback. Carrying on towards a goal he fails to reach, endlessly pushing forward, while everyone behind him lies dying.
The passage from the Bible that Kotomine recites at the end of Episode 23? Psalms 23.
The episode featuring his death aired on June 10th, the date of his historical death.
Angra Mainyu comparing itself to Kiritsugu isn't a Stealth Insult or just a case of Harsher in Hindsight (in light of Kiritsugu's below quote); it makes perfect sense when one is familiar with Fate/stay night, which reveals that Angra Mainyu is not in truth an ancient all-powerful evil deity, but a random, average man from a village in the middle of nowhere who was chosen as a scapegoat by the village to carry 'all the evil in the world' in hopes that someone taking all of it upon himself will save the rest of the village from sin. It's origins is a normal man that turned into a monster to save people. Much like Kiritsugu, except that he made himself into the scapegoat intentionally.
Game Breaker: Gilgamesh. He's canonically the strongest possible Servant and Tokiomi had every reason to believe he had instantly won the War by summoning him. He has stats comparable to Saber or Berserker, 1 B(A+), A and 1 A+ level skills (respective Divinity (which would be higher if he didn't hate the gods), Golden Rule and Charisma), and 2 Noble Phantasms that can only be described as blatantly overpowered. Gate of Babylon give him access to any Noble Phantasm with a physical form (except Excalibur and Avalon, although he has the stronger prototype of the former) and Ea is capable of destroying the entire world at best,and overpowering Excalibur at worst. If his Pride didn't hold him back from fighting at full power, he could've ended the War in a matter of hours after it's beginning.
Careful observation in the anime will reveal some easy-to-overlook but brilliant details for lovers of Cool Planes: The F-15 that Berserker turns into a Noble Phantasm is shown activating the afterburners, thrust vectoring (which the actual plane, or at least that particular model of the F-15, simply can't do but thanks to Berserker's ability actively changing and enhancing the jet can), and crippling the Vimana using the jet's ECM package.For bonus points, several of the maneuvers Berserker pulls are actual dogfighting maneuvers.
Harsher in Hindsight: Kiritsugu Emiya: "Even if I am to carry ‘all the evils of this world’—it won’t matter. If that can save the world, then I’d gladly accept it." Fate/stay night has already revealed (and Fate/Zero will reveal later) that, having been immersed in the mud of Angra Mainyu, he bore, and after five years died from, the curse of All the Evils of This World.
On a similar note, the narration for Kiritsugu's death, seen from Shirou's point of view in the sequel, reveals that Kiritsugu allowed Shirou to take on his dream because he died fully believing that he won't turn out the same as him, and that's why he was able to die peacefully. Not only is Archer more or less Kiritsugu with swords and bows instead of guns, Shirou quite explicitly becomes Kiritsugu in one of the Bad Ends of Heaven's Feel.
Also, the episode where Kiritsugu was forced to kill Natalia, whom he considered a surrogate mother, aired on Mother's Day.
Somehow manages to happen again when Kiritsugu kills Iri and Ilya (Or rather the Grail's illusions of them). That episode aired on Father's Day.
Kiritsugu and Irisviel's final meeting manages to do this thrice in rapid succession. Irisviel wishes for Ilya to come see Japan someday (she does... as another Einzbern tool of war doomed to die), for her to see the cherry blossoms (which can be seen as a reference to the Tragic Dream in Heaven's Feel route) and the summer clouds (Shirou staring at the summer clouds while thinking about his loss and about how his life changed is a scene people might remember from the epilogue of the Fate route).
Even worse, later on, when Irisviel talks with Maiya, she hopes for the Fourth War to be the final one... so that Ilya won't have to take her place in the next one should they fail. Her asking Kiritsugu to bring Ilya to Japan is doubly effective because after the end of the war, Kiritsugu spends several of the last years of his life trying to do that and failed because the Einzberns won't let him, and due to the curse he was too weak to break through their defenses.
There had been several inevitable jokes on messageboards about Saber and the Black Knight involving Monty Python. It's revealed that the servant Black Knight's true identity is Lancelot. In Monty Python and the Holy Grail, John Cleese played both Lancelot AND the Black Knight.
Ho Yay: Kirei and Gilgamesh, Caster and Uryuu (Takeuchi even says that they "should get married already"), and Rider and Waver (who get an official 4koma implying they restored mana that way). Especially since both Rider and Caster are canonically bisexual, not to mention Gilgamesh's relationship with his friend Enkidu was brimming with homoeroticism in the original epic. And that Gilgamesh's image song is basically him mourning Enkidu. Berserker and Kariya also have a bit with the brief blood-sucking scene they get.
It helps that Gilgamesh has been officially out of the closet with his pansexuality since F/HA and that he's from an era and culture when there were very different views on sexual orientation than today. Not to mention that one of the Type-Moon running gags is having Waver Velvet (old or young) totally ignore women who make moves on him such as Fate/stay night's Rider in a Drama CD (who as of Fate/hollow ataraxia is quite firmly established as Bi the Way).
I Knew It: The fan theory that Berserker, the "Black Knight", is Lancelot.
Iron Woobie: Irisviel. The matter-of-fact, almost cheerful way in which she explains that her body has degraded too much for her to use magic alone, engage in her favourite hobbies, or even dress herself without considerable effort is downright heartbreaking.
It Gets Better: Some people dismiss the anime after watching the first episode, which consists of forty minutes of introductions and Info Dump. However, after that episode, things start to really pick up.
Les Yay: Saber and Irisviel have a knight-and-lady relationship, and Irisviel treats Saber less like a tool and more like a human being, similar to Shirou's future attitude towards Saber. Irisviel was a little bit too enthusiastic when dressing Saber as a Bifauxnen. Also, Irisviel holds Avalon within her, which works strongest when Saber is in close proximity—after the fight with Kirei, where Irisviel lay mortally wounded, Saber's presence literally saved her life.
Love to Hate: Caster. In fact, even himself and his Master Uryuu discuss how they are exactly this, being the villains in the great act that God writes. Then just to make their point, they summon Cthulhu-esque Eldritch Abomination to spite God while "remaining aware" of their "role". Goddammit, Caster.
Magnificent Bastard: Kiritsugu's guile and pragmatism leads to some stunningly vicious planning, with himself and Saber as the most powerful pieces. Kirei becomes this near the end.
WAGA ARU G Explanation Lancer consistently refers to Kayneth with "waga aruji", or "milord".
Being Lancer is suffering.Explanation There is a perception in the fandom that Lancers tend to meet terrible ends. It didn't help that both Lancers have E-Rank Luck, making them each a Cosmic Plaything. The phrase "Being x is suffering" itself was borrowed from the Puella Magi Madoka Magica community.
Yuetsu! Explanation The Japanese word for "pleasure", alternatively translated as "joy" or "entertainment"; one of the plotlines involves Gilgamesh making Kirei realize what exactly the source of these things is for him. It's probably a result of the frequent use and the Ho Yay that comes with it that made it into a memetic word among the fandom.
REJOICE, insert character name here. Explanation Kirei Kotomine's line towards Shirou at the start of Fate/stay night has turned into a memetic Catch Phrase for the priest.
(Insert violent sequence here): (IT'S) MORE FUN◊ IN THE PHILIPPINES!◊ Explanation It's a reference to both the Philippines' current tourism slogan, and the revelation that Alimango Island, where Kiritsugu's Start of Darkness took place, is an actual location from that country. Needless to say, a number of Filipinos couldn't resist.
Memetic Molester: Kotomine's obsession with Kiritsugu (and to a lesser but no more insignificant degree, Kariya) gets milked for all it's worth on Pixiv.
There is no way your Mommy can be this cute, can she Ilya?
Moral Event Horizon: In-universe example: Saber thinks Kiritsugu crossed it and calls him out on it when he forces Kayneth to have his own Servant commit suicide; Kiritsugu justifies it by invoking Necessarily Evil and War Is Hell. Also an out-of-universe example, for some.
Caster also crosses this line in record time, by killing a child after giving him a brief moment of hopeone minute after summoning.
Kirei is highly complex, and whether or when he crossed it in Fate/Zero can be debated, but his murder of Tokiomi (though some see him as an Asshole Victim) who deeply trusted him, could count... however, where he really seals the deal is when he uses Tokiomi's corpse to drive a wedge between Aoi and Kariya For the Evulz, which ends up in the latter strangling the former.
Narm: Berserker's battle cries in the anime sound more like the mooing of a cow as opposed to a menacing scream one would expect.
Nausea Fuel: The animated version gives us a long, hard look at what Zouken did to Sakura in the first episode. Insects, Bugs, Worms, oh my. Y I K E S.
Special Effects Failure: The integration of the CG and Hand-Drawn animation can be... spotty sometimes. The opening minute of Episode 6 and Berserker in particular, although the Berserker case may be an intentional attempt to convey just how wrong he and his armor feel.
Berserker may also count, just based on the incredibly awesome shit he pulls off despite being supposedly too screwed up in the head to fucking THINK STRAIGHT, never mind fighting tactically the way he does. The fact that he makes a weapon out of a jet alone despite his mental handicap practically makes him a shoo-in for this.
The Woobie: Subverted by Kayneth. After his moment of Break the Haughty by Kiritsugu, he finds his body crippled and his spirit broken, desperately dreaming of still winning the War, while his Servant causes him trouble and his fiancee is obviously madly in love with said Servant and probably planning to run away with him. In that situation, it's not all that hard too feel kinda sorry for the guy, but he ruins it shortly thereafter by showing us that people apparently don't change that easily, since he kicks the dog by murdering Kotomine's father just to get at the extra Command Spell and stay in the Grail War.
Technically, Kayneth was getting the Command Seal because he was claiming the bounty for Caster. He killed Risei to ensure that nobody else would be able to obtain additional Command Seals from him, specifically using a gun to implicate Kiritsugu, though that part doesn't work out.
Kariya Matou. Severely contaminated with the same worms which permeate Sakura's body, constantly forced to undergo Body Horror to participate in the Grail War, and in the end, he was barely acknowledged as a participant of the war or as an opponent to Tokiomi. And Sakura, whose freedom was his reason for joining the war, stays in Zouken Matou's clutches, further demoralized by Kariya's failure.