The first launch of the Edelweiss. Many a fist was pumped into the air.
Made even more awesome by the fact that it manages to arrive while Alicia and the Town Watch were heroically holding the line on foot against an imperial tank to allow the Bruhl citizens to evacuate safely (which is a CMOA for Alicia).
It's also one for Isara specifically, because she is doing three extremely complicated tasks - driving the Edelweiss, handling the radio net, and delivering a baby - perfectly, without any training, and doesn't even sound slightly flustered.
All of Operation Cloudburst. When Largo and Rosie pick on Isara simply for being a Darcsen, Welkin makes a bet with them: He retakes the bridge in 48 hours, and they listen to his orders whether they like it or not. Welkin then proceeds to drive his tank through the stinkin' RIVER to the enemy camp on the other side. The fact that he learned the appropriate spot where the water is the shallowest "by observing some weeds in the river" gives it a bonus multiplier. In less than two days, Welkin manages to lure every imperial Soldier to the drawbridge and dump all of them in the sink, cementing Welkin's position as THE Squad Seven Commander.
And Welkin again, in the ending. With the Marmota in flames and no way out for him and Alicia, and his troopers refuse to leave them and get to safety. His response?
In the Behind Her Blue FlameDLC; Johann running out into the battlefield under heavy fire to save Selvaria when she's been incapacitated by poison gas, in spite of his fears of being on the front lines. This action gets him promoted to an ace, and he becomes Oswald the Iron.
Edy in her DLC, first her decision to help defend the town, despite being outnumbered, and then later running from one side of the map to the other, through enemy lines, in order to save her "rival", Rosie, who's been injured.
In the same DLC, Homer actually pulls a subverted Cooldown Hug on her by slapping her in the face when she has one of her famous panic attacks when she learns that Rosie's in a bad way. How does Edy repay him? Slugging him in the chin, and then thanking him. Absolute genius.
Selvaria destroying Ghirlandaio using the Valkyria's Final Flame, blowing herself up along with an entire fortress and a good chunk of Gallia's main army in the process. It doubles as a Tear Jerker, and triples as a Dying Moment of Awesome.
Selvaria gets another one earlier, when she effortlessly deflects a tank shot with her weapon.
Bringing down the Batomys super-heavy tank in Chapter 7, forcing the Imperials (including Selvaria in Valkyria mode) to retreat. Squad 7 does this by first destroying its MG turrets, then climbing on it and blowing up its radiators to disable it.
Let's not forget the snipers in that same chapter, who are capable of wiping out all of the starting foot soldiers on the first turn, as well the fact that they could wipe out Selvaria's squad in a single turn as well (not including her, of course.)
It is actually possible to pull off some awesome moves in-game, though a lot of luck or Level Grinding is required to do so. This can range from scouts slipping behind enemy lines to take their camps or take out groups of unsuspecting enemies with a well-placed grenade, shocktroopers charging in and killing entire rows of enemies, lancers actually managing to snipe the radiator of an enemy tank, oneshotting even heavy tanks, or snipers taking out entire platoons.
Welkin's submarine tank drive is repeated in Episode 3 (with water leaking worryingly into the passenger compartment), he and Isara then top it by driving the tank right up the incredibly steep embankment.
The events of Episode 11. Welkin, Faldio, Ramal, and Isara teaming up with Selvaria, Jaeger, and Karl who would rescue Alicia and Cordelia from the kidnappers. Take note that these groups are on the opposing sides of the war. And they're badass in their own rights so when they team up, you know epic beat down will ensue on the kidnappers.
The game being released on steam, to over 90% positive reviews, and became the top download the day of its release, even beating out Assassin's Creed: Unity! The fact it, that a port of a Japanese console game (which are infamous for just not caring about PC in general), ran considerably better at release than AS:U certainly helped.