Thank you. I posted your question on Aviation Lovers and I got this answer: Miami to Narita is about 7000nm, the B777-200LR has longer range than the B777-300ER, 9400nm compare to 7800nm. Also the B772LR is the longest range airliner in the world so non-stop service from Miami to Japan is possible, just not economically efficient.
Thank you very much guys for information about flying non stop to Asia, we are exited that soon Qatar will star flying to Doha from Miami. And American wants South Africa, so happy that Miami keep getting more international city.