If you observe Felix with other characters in the game, he's always got his guard up and generally avoids being around them. His tsundere shit is also borderline toxic
due to how he seldom drops that act. The other characters always seek him out first, and during the conversations he's always seen trying to get out of hanging out, or is insulting them.
Annette though, Felix is the one who purposely finds her to spend time with her and does not put up a wall around her. Annette is a bit of a ditzy loser tbh but their dynamic is cute due to what she does to Felix. I think Annette makes Felix feel safe, which enables him to interact with her without his defense mechanism of being a huge bitch. I also dislike Annette's dynamic with all the other characters so it helps that she has a unique effect on Felix.
My pairings are prob gonna be
Ashe/Mercedes (I hate Mercie but they cook together and it's nice)
Not sure who I'm gonna recruit, Dorothea has been a useful mage and I read she gets a good ending with Petra so might bring them both on board. I'm open to recs on who to recruit!