I think the reason Kai likes Sora so much is because he's the first guy that saw what he sees in Uka. Like even his friends dissed her all the time and questioned his feelings for her. They seemed like they could be best friends.
I love how Uka totally sees the comraderie between them both too and wants to support them being friends. I think she's reminded of Kai when she sees Sora? I think Kai knows she'll feel some type of way for getting between them if she knew or something like that? Thats how i'd take it i guess.
I love coming back and rereading this!! Thx!!