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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."