All Myths Are True: Shirou claims they are, but just not in the same story in order to explain the existence of Rhongomyniad, the spear of King Arthur to Guinevere, who had made it up as a part of Arthur's (Artus's) legend.
Asskicking Equals Authority: All Campione are this by default, but Luo Hao takes it a step further and bases her entire philosophy of Kingship around this concept: 'since Luo Hao is the greatest warrior in China, then shouldn't Luo Hao be entitled to rule it?' is her opinion on the matter.
Animal Motifs: The majority of the Authorities are often associated with certain animals by Campione.
Badass Boast: "I'm not Steel...I am Sword, I'm the Steel that has been refined and forged, hammered and tempered. Given form, given purpose. I'm the Strongest Steel."
Blasphemous Boast: Borderline when one understands the meaning of Steel and Strongest Steel in Campione. Steel is the domain solely of Hero Gods while the Strongest Steel is Artus, the most powerful Steel god. Shirou unknowingly declared himself superior to the King of the End.
Big Brother Instinct: Shirou, BIG TIME. Considering that he literally has godlike powers, woe betide ANYONE who hurts Illya. Godou himself says that this is a zero percent chance that Illya would ever be in his nonexistent (to him) harem because of this.
Is also applicable to Apollo, whose acting as many gods over his divine carreer allowed him for numerous tangentially powers, such as music, healing, and archery.
"The bow, poetry, plague, medicine, the sun, music, prophecy, you have so many Authorities and yet there seems to be little connection between them. However when one learns your other names and aspects then it becomes clearer." ~ Kusanagi Godou, upon unleashing his Warrior Authority (aka Golden Swords) on Apollo.
Composite Character: Shirou is an odd variation. Archer had synchronized with the Shirous in Fate and Unlimited Blade Works, their memories being stored in his soul. When Shirou became a Campione the memories of both Shirous and Archer were integrated into Shirou's mind.
Mordred, the Knight of Betrayal is revealed to be the amalgamation of several war gods such us Laran, Ares, and Mars. Which is pretty much a standard in the Campione!Verse, although it is noted that if he was to return to his myth the modern distinction between them would cause him to separate into the component gods.
Played for Laughs with the curb-stomp NEGOTIATION that happened to Koizumi Watanabe. With the entire "discussion" being full of Entertainingly Wrong and yet perfectly logical, he even lampshades the fact that absolutely lost to Shirou. He was only saved because Shirou thought he was ill.
Doorstopper: As of chapter 21 (Jan 2014) the story is closing in on 500k words. Narrative Filigree is a large factor in this. Chapters 20 and 21 together are the length of a short novel and cover just one extended fight scene.
Empathic Weapon: Shirou's Noble Phantasms in general are like this due to how he makes near-perfect copies of them.
Entertainingly Wrong: Featured heavily. The History Compilation Committee theorizes that Shirou and Illya are the apprentices of a hermetical mage among other things. Meanwhile Shirou believes the HCC to be similar to the Mage Association and prepares accordingly.
The entirety of Watanabe's negotiation with Shirou.
Evil Counterpart: Mordred is one for Shirou. Both are considered fakers who can fight against the originals and possibly win. Both invoke themselves into steel. Also, Mordred's line against Guinevere resembles that of Shirou's when he faces Gilgamesh in the UBW route.
Harmless Villain: Apollo again. After spending a lot of chapters just to summon him, he got defeated by Godou just one chapter after his appearance. This is after Athena thinks of him of dangerous because he seems to not care about pride and just going for the kill. He doesn't, he spends most of his time gloating at Godou when he should have just kill him.
Kaida upon hearing that Shirou, a godlike Campione with the rights of a King, cannot meet her because he went to school, she has a destructive cycle of circular logic about expecting the unexpected. She was told to expect it, but that was unexpected, but she did expect it...
After mistakenly calling out Shirou, Luo Hao is lost. Since she was wrong, she must protect her honor through violence. On the other hand, because she swore an oath of peace, she must uphold her honor through non-violence. But she has to because of her honor, but she can't because of her honor...
Made of Indestructium: Somehow, Shirou's cellphone survives all the punishment of his battle with Mordred.
Mass "Oh, Crap!": The entire mage community has this after learning about Shirou inviting THREE CAMPIONE to his mansion.
Monty Haul: The entire mage community sees the Feast of Kings as an amazing event. After an incredible battle of four Campione versus four Heretic Gods, Shirou invites the four Campione to a banquet with amazing food and drink, a contest of kings and, the most mind-boggling part, legendary weapons for all those attending.
Mundane Utility: Shirou uses two Noble Phantasms as a light source and a fountain. He lampshades it.
And again, when he ended up inviting Guinevere as well.
Guinevere has one of her own when she accepts said invitation.
Mythology Gag: When Shirou's watchers from the History Compilation Committee appear in their maid uniforms, Illya's newly discovered maid switch is triggered.
More than Mind Control: Venus attempts this with Arrows of Eros on Shirou, and then with Heart's Thief. In the end, she isn't entirely successful, and is left with her Authorities fully tapped, and a brainwashed Shirou under her control. Word of God is Shirou is effectively under a variation of Mad Enhancement like Heracles was.
Venus manages a form of this, in the end it was her threatening to kill Sakura that finally allowed Shirou to overcome her Heart Thief Authority
Otaku: Illya, having been overexposed to modern entertainment, now uses her new skills as a Meta Girl to get personal entertainment from Godoh and his harem. It's affected her taste in naming as well...
Only SaneCampione: Shirou's first undead Servant, Yusuke, believes that Japan has a monopoly on these after meeting Luo Hao.
The Power of Love: After two monster sized chapters of fighting, it wasn't Luo Hao's martial prowess or Kusanagi's dogged determinism that overcomes Venuses hold over Shirou, but his all consuming love of Sakura that won the day.
Shirou was only able to draw Lancelot's sword because his love of Guinevere was so deeply imprinted on the blade that it actually helped Shirou bring itself into existence so it could defend her.
Serious Business: Meta-Example. The author has alienated several Nasuverse fans with rather lax handling of Nasuverse mechanics. He even managed to hit the Fandom Berserk Button by mentioning in an Author's note his belief that Campiones are capable of defeating Gilgamesh and TYPES/Aristoteles. He quickly retracted these statements after being pressured by angry reviewers into doing more in depth research into what he's talking about.
Spit Take: Shirou's reaction to hearing about Illya's first day of Tea Ceremony lessons.
—> "Kusanagi-san has added another girl to his harem."
Hilariously, Illya was trying to see if he would Spit Take.
Split Personality: Shirou adopts a fake persona he calls The Fake King when conversing with Campione, the Committee and other important magical figures. Recent chapters, however, have him slip into it subconciously.
You Watch Too Much X: Shirou worries Ilya may be watching too much anime whenever she starts making parallels between their life and common anime tropes. Even Ilya thinks this when she catches herself debating whether Godoh or Shirou is the protagonist during a pitched battle.