As absurdly backwards as it may seem, I agree with KrayZ33. Rika actually comes off as the most "normal" of the girls.

Sure, she's the worst kind of fujoshi, reads her mecha porn aloud, tries to get Kodaka to have sex with her, wastes no time in feeling Yukimura up in a public hallway, tells the others that she has to go to the "Rika Room" and masturbate on a desk or something...

...but she actually seems to understand what normal social behavior is meant to be. She just doesn't really care most of the time.

In this recent episode, when Sena stupidly tries to get back at Yozora by doing exactly what she did back to her, laughing snidely at all the same points, putting in the random name, etc., Rika confronts her directly. Not in a particularly crazy way, but more of a, "Why would you even think that is appropriate way to act after the way you're treated? Do you not realize that getting Yozora to play games benefits you too?"

Aside from the overt attempts at getting Kodaka to like her fuck her, she changes her hair to draw his attention once she realizes that she is his type (since he did admit it). That's a fairly normal thing to do. Maybe not to the extreme where she dyed it blond, but she's definitely trying to pinpoint his preferences, another frequently used tactic by "normals." Compare that to Yozora, who feels that she only way she and Kodaka can continue their friendship or go beyond that is if the two of them are completely alone. Or Sena, who is too stupid to realize it. Or Kobato, who obviously wants to monopolize him.

She's weird as hell, sure, but I think that she, "gets it," the way that the others don't.

Yukimura might be on her way there too, now that she comprehends that she is, in fact, a girl. It already feels like Yukimura is pretty happy with the "more natural" relationship available to her, instead of the samurai-page love affair approach she was going with (see episode 13, the group story writing event).