VA plane doing this route is only a 737, so has limited seating, and limited fuel capacity.
Plus the number of crew too, ie, only 4 if its not the same pilots and FO doing the flight up, and then coming back down, or if the flight is carrying the pilot and FO of the return flight, or will they stay up there in HND for the overnight, before piloting the next days flight back down, if its not the same crew doing the flight up and down again.
ANA using the 787 has got a wider plane, so their capacity is even higher still, so their planes can carry more pax and also have the extra capacity for freight, which the VA 737 would be tight about.
If for some reason, they need to pick up extra fuel, it would have to be a country on the route, some say its unlikely the plane would need to make any stops, but what if.
Its hard, they want to be mid range, but the impression I get, is that its more a glorified JQ similar.
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What else to say, even JQ is using their 787 on the CNS - NRT routing.