If you're in Waikiki or at any of the major tourist sites like Hanauma Bay, you are mainly seeing tourists from Japan who don't live there. They go to Hawaii because it's the closest part of the U.S.A. to Japan and because it's beautiful and because they can buy name brand things for cheaper in Hawaii than in Japan.

But if you go to the beaches on the north shore or Kailua or outside of Honolulu in general, you will see surprisingly few Japanese tourists compared to Waikiki. That's because they mostly stay with Japanese tours that take them to specific tourist sites, or else they stay in Waikiki for shopping and dining. (The outer islands also have relatively few Japanese tourists.)

There are also local residents in Hawaii who are of Japanese ancestry. Their parents, grandparents, and great grandparents came to Hawaii to work in agriculture or business. Honolulu has a much higher percentage of locals of Japanese or Chinese ancestry than the rest of the Oahu does.

Both are close and climate is different