Was flying to the states from Vietnam via American Airlines and the stretch from Hanoi to Tokyo was operated by Japan airlines. We were supposed to be in the economy class, but got upgraded for free to premium economy and it was literally the best plane ride I've ever been on. Free wine, Free Udon noodles, great in-flight entertainment (with noise-canceling headphones) and ample space. The seats recline super far, with a fold-down foot rest and flip up leg rest. The arm rests are quite wide, so you don't have to jostle with your neighbor for elbow room -- plus there's a partition at head level so you have a good amount of privacy.
Couldn't be happier with the flight. Arigato!!!!