In Regards to that Kai Hibbard Thing: Just because her name means something in Japanese, doesn't mean her parents read through a Japanese/English dictionary looking for baby names. Her parents probably thought itt was just a pretty name.
Last names aren't determined by race, they're determined by ethnicity. That being said, no one can have a 'caucasian last name'. They could have a French, Welsh, or Polish last name, but not a Caucasian last name. And why do you assume everyone is caucasian? I sense a very distinct Latin vibe from Kairi, but that's just me.
CelestialStarDust is right, Japanese names could work anywhere.
QFT