Right now in the anime thread there's a discussion going on about Rei's reaction to Shidou, wanting to leave him and his students behind when escaping with the bus. This is somewhat hard to discuss in the anime thread without referencing what happens later on in volume 4
So we all know Shidou is a real piece of work, but is Rei's reaction of wanting to abandon him to certain death really justified? Or her desire to shoot him later on in volume 4, for that matter. When I was reading volume 1 for the first time I thought that Shidou must have raped her or done some similarly evil deed, but later we learn that all he did was get her held back a grade. Unfair, yes, immoral, yes, perhaps even damaging her future career prospects to some degree (doubtful) - but a far cry from the kind of emotional scars that she's showing, and probably not an act worthy of being indirectly killed for along with a group of completely unrelated students. That whole "it's your fault that I.... got held back a year" was rather anti-climatic.
Of course, since it's the apocalypse, she can do what she wants pretty much, but being one of the protagonists means she shouldn't do anything too evil
But then she wanted to take the baton to the guy who nearly raped her in volume 2, also. Maybe she is somehow getting into the whole enjoyment of violence thing, like Takashi and Saeko are?