Just a guess, but in the few instances I've seen manga use a literal "the", it's kinda used to indicate someone's infamous for a certain trait, kinda like how the West would use it. (eg. you're not just a baka, you're ZA baka.) Don't often see it used without it being mentioned in any dialogue, though, though I don't have the JP to check it against. If I had to guess, it's that Akari see Kana as "THE Kakana". But don't quote me on it.