Welcome, Xirchs the 13th, Endless Warrior Sora
Well. Hm.
It's interesting.
Though, Riku was possessed by Ansem SoD and that pretty much accounts for everything --being violent and whatnot-- that he did.
That's not the case, really. Riku fell into Darkness on his own accord as far as we know, and then kept falling all but willingly - because seriously, even with Maleficent telling him Sora didn't care anymore, one should think the guy should get over it and trust his best friend for years a little bit more.
Riku fell on his own - Ansem took advantage of that to possess him, not cause it.
Because in CoM he was able to think and make choices between his friends and the darkness, I think Kairi could do the same with light.
Only Riku had a "wake up call" Kairi's yet to receive - which would be realizing what she's done at the end of the road in which she was certain she was on the right path.
If not, Kairi angst is always awesome, say for like not having darkness in her like everyone else or having to fight against Sora. That would be a good place to make her character more 3-dimensional.
Well, if she'd really get "Blinded", I'd see her more as certain she was trying to save him - while, ironically, giving him a beating as one of the final bosses, or at least a main one.
It would be interesting to see her stand off against Riku, what with him being the Darker one of the two.
Oooh, and Anti Form! If she'll really lose it, I can see her popping a vein.
It's doubtful, though, that she would ignore Sora if he convinced her that darkness is everywhere and you can't really fight it, etc, etc.
Only she'd be kind of out of reach like that, much like Riku was rather early on in KH1. Sora effin argued with Donald about taking Riku along but Riku still took off and was prissy about it.
That's the point about being swallowed by the Darkness - or being Blinded by the Light. It means the truth can't reach you.
She'd sooner wave it off as Sora being "Affected" than listen, should it get to that.