developmentWhen introduced, Kairi is very much still a child. She's quite naive. She's a little rebellious, very much laid back, and she gets out of the hard work when she can – like Sora, she's very light hearted and just enjoys having fun. The thing is, Kairi's also smart. She may be laid back but in no way is she immature. She knows her friendship with Sora and Riku can't last as it has forever, and that there is a rift forming inbetween them – she might not be aware of the sources exactly, but she's wise enough to notice that something's been amiss for some time. It's likely difficult for her, with her two best friends vying for her attention when she just wants to go on as they always have… but even so, she still truly cares about the both of them.
If anything pushes her into maturity and seriousness, it's the time she spends alone. The very, very lonely year, waiting for Sora, forgetting everything about Sora and practically losing her identity - which I personally feel fandom is so quick to forget about those hardships she went through - and even after all that, she still waits, she's still loyal, because at the centre of everything, that's what Kairi is. The most loyal friend you could every ask for, that will always have you back, no matter what happens, no matter what you do. She's no longer as laid back, and is more softspoken and introspective than she was before.
When we first meet her, Kairi strikes me as very much the type to go with the flow, in order to not rock the boat, which makes her somewhat passive. She's not particular defensive and is never offensive - well, unless she has to protect those she cares about the most. Her pacifistic nature melts away to a brave, courageous young woman who will fight even if she knows very little of fighting, and that only branches over into speaking out for what she wants and what she wants to do. In the first game, she's rather sassy, which is replaced by being demure, but the truth is, I don't think it's ever quite gone away. Kairi's done her period of waiting, and done it beautifully, and now she's ready to take destiny into her own hands. Like everyone, she's just grown up, and bettered herself, though much of this is unseen. But by no means was it easy or simple. Sora had the adventure, Riku battled himself, but Kairi grew, too. Kairi changed. Where once we had a girl who did not mind, who was non-committal, now, she knows what she wants and she will go and get it. She wants to protect her friends. She will protect her friends. She's a damsel, she's in distress, and she can totally handle it. She'll rise to the challenge.
Better yet, she'll shine.