She's sometimes seen as the archetypal tsundere, her (perceived) opposition to Rei paving the road to a thousand standoffs between tsundere and kuudere, such as Nagato vs Haruhi; but it doesn't seem right to me. Firstly because Nadia, from Anno's previous anime was much more of a tsundere, but also Asuka never felt like a tsundere to me in the first place; and I think I just found the words to explain why. She definitely has the "tsun"; she is hostile to the point of aggression towards Shinji, and it would also seems that she might be interested in him romantically (the "dere"). However, she lacks a causal relation between the two. See, the idea of a tsundere is that her hostility serves to hide the romantic feeling towards its object, which she doesn't want to admit. Asuna, however, isn't bashful about love. She has no qualms hitting on Kaji or kissing Shinji. The cause of her hostility is another feeling she represses and that's seeing herself in Shinji. The need she feels to be strong, talented, perfect, and getting praised for it is a huge part of her character; which is why she does away with any doubt or weakness. But Shinji is a reflection of all these weaknesses, and he doesn't have the "decency" to hide it like she does, and that's what makes him unbearable to her. And yet, perhaps some part of her wishes she could let herself be weak like he does. Like the widely hated line "What, don't to kiss a girl on the day of your mother's death?", she's making fun of supposed mommy issues Shinji might have, but really making light of her own mommy issues to help her dominate them. I think this plays intoher aggressive tendencies much more than romantic feelings, hence why I find the term "tsundere" less than appropriate.