This is the first half of my son's name. Kai is VERY popular in Hawaiian. Can be used for lots of names. My son's name is Kainalu which means ocean wave. We also know a Kaiola, a Kainoa, Kaiemi, Kainani, etc.
When I was in middle school I heard this name for the first time and I fell in love with it. I always come back to it for a name. Unfortunately it doesn't flow at all with my maiden name or my married name or I would absolutely use it.