Qantas and United Air. But take Qantas because the American airlines are all disgusting. Why would you want to go to that country anyway. Waste of money
United and its partners - now that it has merged with Continental and has access to the Guam hub, flies to 12 Japanese cities. Sapporo Chitose, Sendai, Niigata, Komatsu, Tokyo Narita, Nagoya Chuba...
It depend really. Qantas's hubs are all over Australia especially Sydney.
Sydney flights that are the best:
Qantas
Singapore Airlines
Emirates
British Airways
Virgin Airways
All 4-5* airlines
From the major ports , ie Melbourne Australia and Tokyo Japan it is roughly 10 hours 20 minutes. However, the shortest flight time possible is from Darwin to Kagoshima - clocked at just over 4 hours.