I assume you'll be flying economy. If that's the case, I can tell you about United as I just flew United from KIX
The last couple of times I travelled to Japan from the U.S., I flew business class, so I was kind of dreading economy class. I was pleasantly surprised, however.
The seats were pretty comfortable, and I believe they had recently been recovered in some kind of dark teal fabric. I was on a 777, so there were PTVs at every seat. This was a nice feature, but I wasn't really interested in any of the movies that were showing. There was a nice blanket and a pillow at each seat.
The food was better than I had expected. We were offered 2 meals and a snack. The first meal was a choice of chicken katsu on rice and curry or beef and potatoes. I chose the former, and it was actually really good. It came with a kind of boring salad (really just lettuce), a small cup of thousand island dressing, edamame, a piece of salami or something, caramel cake, a roll, and a cup of water. The midflight snack was a small bowl of instant ramen (which I brought home and ate later), an almond cookie, and another cup of water. The ramen was actually high quality instant ramen (which might sound like an oxymoron, but there is such a thing). It was made by Toyo Suisan (I believe) and it had pieces of fried tofu and green onions in it. The final meal came about 1 hour before landing. We had a choice of an omelet or pasta. The pasta looked like it had some cheese and regular tomato sauce on it. The omelet was very thick and it resembled unsweet Japanese tamagoyaki. It wasn't bad, but it wasn't exactly great either. It came with 3 pieces of potato and a micro-sausage which was tiny but tasty.
I hope that was helpful.. Let me know if you have any other questions.