Kaden and Valyn's reunion after eight years of separation, especially Valyn tackling his brother in a fierce hug. After spending the latter half of the book as a stoic soldier, Kaden's presence just seems to take him back, just a little, to their childhood. Doubles as a Tearjerker because Kaden has gone into the vaniate and thus switched off his emotions, so he can only respond to Valyn's affection with cold dismissal.
After spending several chapters bickering, blaming each other and generally not getting along, it's heartening to see Valyn's Wing come together as Fire-Forged Friends, not even questioning Valyn's revelation about the conspiracy against his family, not to mention Annick's admission of innocence and her coming out before uniting to save Kaden.
In the online short story The Last Abbot of Ashk'lan, Akiil's determination to find and protect Kaden, even risking his own life, despite his own strict policy about looking out for number one first and foremost.
Valyn and Ha Lin's first kiss. They're hardened soldiers trained in ways most kids their age can't even imagine, but in that moment, they're just a pair of young people with strong feelings for one another. Valyn thinks later that even if Kettral code prevents them from officially being together, they can still spend the rest of their lives fighting together as part of the same Wing.