Marisa's recruitment on Eirika's route certainly qualifies, especially considering her Establishing Character Moment was her coolly asking her employer to just point her at the people she needed to kill.
Gerik: Is that you, Marisa?
Gerik: What a mess... Looks like the guild bungled. They're usually diligent about making sure this sort of thing doesn't happen. But here we are, two people of the same troop, working for opposite sides.
Natasha: On what? If this is another of your little jokes, I—
Joshua: Will I make you happy? That's what we'll bet on. Are you in, or what?
Joshua: That's everything I've got. I can't up the ante any more. So how about it? Are you in?
Also, their ending: "When Joshua returned to Jehanna, he took Natasha as his bride and claimed the throne as its rightful heir. Natasha was the perfect companion, and together, they carried the mighty desert nation to great glory."
Forde and Franz' supports. Franz is known for his light-heartedness and admiration of Seth, so Forde is certainly surprised when Franz tells him HE is his role model and not Seth, despite Forde's insistence that there are better role models. It ends with the two of them vowing to rebuild their lives when the war is over.
Amelia and Duessel's A support reveals that Amelia's mother is alive and well. Sometime after she was abducted, Duessel and several other knights took down the bandits and rescued her. She was in bad shape and had lost her memories, so he took her to a peaceful village where she recovered and remembered she had a daughter. When he tells Amelia, both of them dissolve in tears of joy and their shared ending has her becoming his most trusted right-hand.
Ephraim saying that Eirika can handle her own in combat in response to Seth telling her to go back to safety is pretty heartwarming.
Their relationship in general counts as this since it's built on their love and trust for each other.