I didn't really like Cynthia at first. I thought she was an annoying little brat who disrespected sumia, until I got completely through the conversation and just felt sorry for her and felt really bad for hating her.
I've yet to encounter a "Zelos" as it were. (I say that because early on, I used to hate Zelos in Tales of Symphonia. He grew on me, and is generally one of my favorite characters.)
Now there is Gameplay!FE9!Astrid. I really didn't like Astrid. Then I discovered "give her a Forged bow" and then OMG. (Sadly, she's irredeemably suck in FE10. (Except Easymode or the Random Number Goddess saying otherwise (First due to Easy mode being Exactly what it says on the tin, and the latter is capable of making anyone a god under any circumstance))
Maybe... Florina? I wasn't all that impressed with the "oh, I'm so clumsy and shy and meek" stereotype of a weak, helpless character. This distaste developed when I played the game for the first time... over 9 years ago, when I was much younger and had far less patience for annoying surface level characters. But through a few supports, and blessings from the RNG goddess, she slowly became one of my most devastating units. Every play through of Blazing Sword now has a safe spot on the team for Florina.
I suppose to be specific, I thought I'd be indifferent to Cynthia. I rarely get annoyed by her type, but if I find their personality a bit much, they go onto my indifferent list. Instead I consider her to be one of the funniest characters in this game, and a friendly, amiable girl.
I also didn't expect Nah to become my favorite character. I didn't really think much of her at first, but as I went through her supports, I found out what a complex character she is (though what the heck is up with some of romantic supports?) and came to respect and adore her.
My 25 Most Favorite Games - http://www.unikgamer.com/members/strawberryeggs-786.html Official Nah of the Fire Emblem: Awakening board.