She and Mina have the main flaw of showing up too late in game to really develop (mina you see more of in backstory and the after game). Still we get enough back story on Kahili to at least know a bit of her (personality is like that of a competitive sports person… something I don't really mind)

Kahili seems to be the super competitive sports player type, which is why she's frowning and upset at losing: she wanted to win, nothing more. That is really all there is to her character though, which really is a shame.

Also, Acerola was the one who replaced Nani, not Kahili. And Acerola calls Nanu "uncle" so they do know each other. (But I heard that they are not actually related)