Was it really out of character?
Given that Rei and Asuka acted differently, I think what it comes down to is that all you had to change was Shinji, and everything else falls in place.
And the end of the world is pretty good way to change your personality. Also, if you didn't like asuka's change, let's face it. Retake asuka was what EoE asuka wanted to be.
If you didn't like how Rei acted, then you don't know Rei very well. Rei was suicidal from the very beginning.