Princess Luna telling Nova what really happened on that fateful night four years before, and reassuring him that his cutie mark isn't for almost killing someone, but for protecting those around him.
Sky Bolt finally deciding to brave it, and kissing Sabra as they are enjoying the scenery in the cockpit of the Hummingbird.
Nova deciding that he is more than a thief, and that he really belongs in the Dusk Guard, calling them his friends.
Steel inviting his old friend Primetail over to a family dinner and their interactions with his family.
Steel and Cappy sharing a kiss.
Sabra returning Sky Bolt's kiss, in The Definition of Strength chapter 2, in gratitude of what she has managed to accomplish for him.
Sabra deciding that, even after he has found his answer, he will stay with the Dusk Guard (though he still plans on sharing his knowledge with the monastery zebra).
Sabra:Here, I am home.
Nova refers to Steel Song as Steel instead of Captain while they are visiting his family for Hearth's Warming, showing how far their friendship has grown.
As they are sitting at the table, Jammer says that giving someone a cutie mark cookie means one cares about the receiver. As Steel and Nova are about to leave, Sparkle, who has spent most of the party hiding from Nova, decides to be brave and gives him a cookie with his cutie mark on it, because she noticed he didn't get one.
Having realized that the creature they are chasing projects and amplifies emotions, Steel faces it and manages to calm the scared filly down, cradling her as she falls asleep. DAAAW!
Especially heartwarming seeing that he had been troubled by the perspective of being a bad parent, and scaring children with his demeanor and tales, just hours earlier.