Another optional one: Euram Barrows' Heel-Face Turn, when he finally decides to stop being a fop and take his duty as the heir of the Barrows Family responsibly.
Arguably, when Logg and Lun ram a burning ship to destroy Hatred Fortress.
Any of Lucretia's plans count for this trope.
If you let Richard duel a Raging Childerich and Guarding at his Super Move, he gets his eyes blinded by the green liquid, but was still able to block ALL of Childerich's strikes! He does this while looking like he's barely even putting any effort on it.
The Prince using the Dawn Rune on Dolph, killing him while saving Lyon.
Sialeeds killing Salum Barrows definitely qualifies, though she appeared to be working for the Godwins at the time.
Lymsleia, who is all of ten, smartly declares to Gizel, her husband that the rebel army merely took advantage of his weaknesses, and then declares that she will end the war by riding into battle herself. The girl's definitely ballsy. The fact that it's a plot she engineered only makes it more awesome, even if it fails due to a defection.
Really, Lym throughout the entirety of the Godwins' occupation. Given everything she's put through, her willing resolve to not shed a tear during the whole ordeal is incredible. Because she doesn't want Gizel and Marscal to win, and if she lets down that last wall and breaks down... they win. And she doesn't give in and break down, not even once, until it's all over, and her brother and her Knights have liberated Sol-Falena and can safely return home to her.