Immigration and customs - when?

I am traveling from Dallas (American Airlines) to Narita (ALL Nippon) to Okinawa.

Will I go through customs and immigration at Narita or in Okinawa?

Last year I went from Dallas to Narita, bus to Haneda, then fly to Okinawa. I had to fill out immigration and customs paperwork at Narita. Is this because I was leaving the airport for Haneda?

You go through Immigration and Customs at Narita.

When you exit customs you recheckin at the domestic departures at Narita Airport, and go through airport security again, for the domestic portion of the flight.

If you have any checked luggage, you have to pick it up for customs clearance, after which you can recheck them, when you check into your ANA flight on the domestic side.