Especially the part where Illya uses Archer's Class Card to draw on Unlimited Blade Works and traces Excalibur!
It's even more awesome animated. All with EMIYA being play in the background.
But don't take our word for it! Watch the whole scene in it's glory here.
Illya utterly destroying not one but all of the Heroic Spirits qualified to be True Assassin single-handed. Yes, the schoolgirl really DID just completely dominate every single person to ever have the title of Hassan-i Sabah. By herself.
And then there was the finisher against Berserker: NINE. EXCALIBURS. AT ONCE!
Chapter 16 of 2wei, even if somewhat not as epic as it could have been: Chloe launching Crane Wing Three Realmnote Yes, the same move Shirou used to defeat Saber Alter against Bazett. And a CMOA for Bazett for all but completely shrugging it off.
Even before that Chloe Forging and using broken Excalibur with avalon as an opening attack against Gilgamesh. It was constantly pointed out in the original time-line and other series that it would take all of Archer's abilities just to manifest it momentarily and it was beyond his scope to even attempt to twist it, and she used both noble phantasm as ammunition in a second without even taxing her. Sure, it didn't even scratch Gilgamesh because he had the "Shield of the Gods" an anti-divinity defense, but it was still the second most broken technique in the franchise.
What made this even more awesome was that she wasn't even transformed when she did it. She had already seen this massive, corrupted monster kill Bazette during the earlier fight (she got better), yet Illya charged in and stood right next to the center of the thing as an ordinary, fragile, ten-year-old girl with no defenses at all, and slapped it in the face.
3rei kicks off shortly with Gilgamesh facing off against Angelica, The Ainsworth with his powers, so most of his arsenal, Not only is Gil able to put up a decent fight once he steals Enkindu back, He is able to make his opponent look like a fool for most of the fight... Then She stops fighting like he would.
End of chapter 4, Beatrice scoffs that This Is Reality to Illya (after she's been torturing Tanaka); which makes Illya realize that both Miyu and Tanaka had responded immediately that "people can't fly." The Crapsack World they're from has FORCED them to believe permanently that they cannot fly, ever. They cannot dream, they cannot hope. This is unacceptable. Then she transforms and announces that she's taking everyone's wings BACK.
An extension of this occurs later when Illya and Kuro are facing down Angelica as well as the brainwashed Rin and Luvia, and Illya is told that she has to make a choice - either she saves Miyu, or she saves the whole world, as if she saves Miyu and foils the Ainsworth's plans, Miyu's world will perish and humanity along with it. Illya, of course, decides to Take a Third Option, declaring that she will save both. Then Illya, Kuro, Bazett and Gil execute their plan, freeing Rin and Luvia and completely outmanoeuvring Angelica, allowing Kuro the chance to destroy the roof and walls of the castle tower where Miyu is being kept, which allows Illya to move in and fake out Darius with a surprise attack with Rule Breaker, exposing him as Julian and allowing Sapphire to reunite with Miyu. This also allows Gil to head underground during the commotion while everyone's attention is on what's going on at the tower and free Miyu's brother.
An offscreen one. Miyu's brother managing to save her and launch her into another world. Meaning that he had to go against the Ainsworth all by himself, and considering that one of them is more than enough to hold off a Servant(heck the Head of the family can literally block Excalibur with one bare HAND for crying out loud!), and they all had Class Cards, He must be a grade A BADASS Motherfucker!
Said brother is quite obviously the parallel universe's version of Shirou. Despite not even being a main character anymore, Shirou is stillGAR when a situation requires him to be.
3rei #23: Miyu's brother - explicitly called Shirou Emiya by Julian - shows his credentials. His opening move? Nine Lives. His next move? Projecting Ig-Alima, a weapon that Gilgamesh notes is a divine weapon. Something which even Archer and Shirou of Fate/Stay Night can't create without killing themselves. All these weapons are formed without him slowing down a bit.
And then we get awesomeness squared in #25: Shirou and Chloe taking on Angelica Using the Gilgamesh class card together. Both of them pull out Kanshou and Bakuya Overedge and they read her next attack in order to get in a sneak attack from below before finishing her off.
Shirou installing the "Faker" Archer class card on to himself and transforming into a mixture of Avenger and Heroic Spirit EMIYA. It's as badass as it sounds. His new look is ten times cooler than that. What does he do with this power? He first starts using his new form to kick the ass of his world's version of Shinji. Unlike Fate/Stay Night, where Shinji is at best beaten verbally by Shirou and at worst overpowered by Shirou with a metal pipe, this Shirou holds nothing back and punches his face in, insults his fighting prowess, pities his very existence, etc. Given that this is Shinji, this was a reckoning long past due.
What happened after he defeated Shinji? "Without a moment to rest, enemies with cards came by one after another." He defeats the next five cards and wins the Holy Grail War IN. ONE. NIGHT.
3rei #43 reveals just what it took for the Ainsworths to capture Shirou. After he creates his own, snow-covered Unlimited Blade Works, he matches and surpasses Angelica's full-power Gate of Babylon, even deflecting her Ig-Alima and Sul-Sagana with his own copies. It took Angelica's own Flash Air - something the normal Gilgamesh does not have - in order for her to dodge a fatal attack and reclaim her advantage, and she ultimately needed to utilize Ea to defeat him. Not only did he survive it, but he was able to successfully accomplish his goal of sending Miyu to safety, essentially claiming victory over the Ainsworths despite his capture. Not even Julian himself tried to stop him when they briefly talked at the end of the grail war despite what we've seen him be able to do.
Not to mention this Shirou is one of the very few people in the entire Nasuverse at this point to make an unambiguously successful wish using the Holy Grail (others being Maris Billy and Solomon in Fate/Grand Order). Though in his case, it went above and beyond the wish he asked of it - Miyu was sent to a world where she not only found new friends and adoptive family who cared for her, and also found happiness with them, those friends were also loyal enough to go through hell and back to save her, but also determined to save her world as well without sacrificing her to do it.
3drei #48: Rin manages to work out the Ainsworth's entire plan by piecing together the things shes seen and heard and knowledge of how a magus like Darius works. This leads her to discovering something important about the alternate universe: that in this universe's history, Pandora's Box was never opened.