^Kairi doesn't show too much affection to Sora. We have to remember that she's the last one who started remembering Sora. I didn't see her bowing before a nobody just so she could see Sora. What does that tell you? looks a little suspicious wouldn't you say. She even fails as a friend. What did she do to go find Sora?
look what Riku did for his brother like friend. He went all the way to the realm of inbetween just to find Sora's nobody so Sora could wake up out of his coma. And no I'm not supporting yaoi here. I'm just saying that Kairi doesn't really care THAT much about Sora. Riku cares about him more than Kairi because well, Sora is Riku's childhood friend.