@Flamelord I haven't seen much of the Railgun anime but from what I remember Ruiko's a pretty nice girl.
Here she seems pretty pissed off and threatening. What happened? o;
An alternate universe happened ;)
Specifically, this Ruiko is from the culmination of my own home brewed version of the Level Upper arc, intended to make it...better/have an actual point. Because power is a hell of a drug, especially for the powerless, the road to hell is paved with good intentions, those who have gotten power where they had none previously are unlikely to willingly give it up, particularly because someone who could basically get away with murder if it weren't for her sense of morality wants it, and because once you're drawn into the Dark Side of Academy City, there's no escape.
Normally yes, she is a pretty nice girl. But you're not catching her when she's 'normal'.
Oh, also being dumped into the multiverse and having the first person she meets be this very imposing/threatening alien doesn't help :p