I've taken lots of flights (over 50) from the east coast of the US to Asia, particularly Japan. I lived in Japan for 7 years. Below are my recommendations for easing the pain, even in coach:
1. If at all possible, don't do a 10 day dive package to Asia from the US or Europe. You will barely be over jet lag before you need to turn around to go home. If you're retired or have loads of vacation time, go for at least a month. Hit several bucket list spots on the same trip. Fly to somewhere at or near the time zone where you'll be doing most of your diving. Spend the first week looking around, meeting people and getting used to the time zone. Next, go diving. Go to another area and do more diving. Now you've completely adjusted to the time zone and starting to settle in to your new life style. If you've been diving in the Philippines, it's now a short flight over to Palau. From there another short flight to Truk. Flying now is a pleasure. Look for liveaboards with discounted last minute openings. I did 12 days in Raja Ampat, 20% off and free nitrox by booking two weeks before departure. We only had 4 guests on a 120 ft. Phinisi boat that holds 16 guests. All these insane dive spots are just a few hours flight from each other... once you're actually in that region.
2. As soon as you book your long flight, try to get an emergency row exit seat, even if you have to pay extra. This becomes crucial for flights over 7 hours. I did a 15 hour flight from LA to Hong Kong recently and I paid about $100 more for an exit seat in coach. This seat had no seats in front of me. Therefore, I had more leg room than business class and could get out of my seat without disturbing anyone. Worth every penny.
3. Depending on the flight, bring your own food. US cross-country flights serve next to nothing. I usually bring a really nice Italian sub cut into sections... or whatever will make you happy and doesn't require refrigeration.
4. When flying in Asia, avoid US carriers. Carriers such as Singapore Air, ANA, JAL, etc. are WAY better. For example, I was flying from Jakarta on, technically, American Airlines to Los Angeles. I was able to get on ANA flights that were a code share with American. If you want to see how service is done right, take an ANA flight. Also, the food is better and there's more of it. Again, get an exit row whenever possible.
5. Get a phone that is unlocked. This means when you arrive in Jakarta, you can get a sim card that works locally and probably has a data plan. When in Japan, I get a portable wifi in the airport and use that to make calls, access the internet, etc. It costs about $8 day. You can do this in most countries.
6. If you're stuck in an airport due to a delay, etc.... ask if you can get into the airline's lounge. You'll be charged a fee but it will probably be worth it. I allowed myself to be bumped off of a Delta flight to Tokyo (got $800 in Amazon credit) but had to wait 5 hours for next flight. Went to Delta lounge, gave them my story, and they said I could use the lounge for $50. Bangin wifi, free food & alcohol, nice big comfy seats, beautiful shower facilities with towels, bathrobe, soap, shampoo, etc. Again, worth every penny.