It is called total eclipse. I can only imagine that wasting some of the world's remaining production capacity on these jokers (including Yui) is what pushes humanity to its darkest point so that the real Muv-Luv Alternative cast are left to try and pick up the pieces.
Yui's cold attitude pisses me off too, mostly because it has become such a cliché. Character gets traumatized, and becomes ultra-serious and a total bitch/asshole. I'll believe she has a right to it when she shows that she can actually fight these days. At least we know the two insane and/or telepathic sisters are one of the best pilot duets at the base. I wager the only thing that will fix Yui is her getting some from Yuuya. And given this franchise, she'll probably die right after that.