For the cross country drive, I would use a bigger carrier or a small cage. This will give home some room to move around, but still keep him safe. Being a pen along so you can let him out at night and when you stop (only if it is safe). Bring enough pellets and hay to last the trip and at least a few days until you can find some there. It is also good to take water from home. Veggies are good to take too, but it would be good to buy fresh when you can.
As far as taking him to Japan, that can be tricky. You would need to find out what the regulations are and if there is a quarantine period. I would not sedate him, he needs to be able to eat and drink during the flight and be able to move around and brace himself if needed. Sedatives can work differently at higher altitudes and with different pressures. It is really not recommended to sedate pets for travel.
If they are bonded, then they should stay together. Get a carrier with lots of room for both of them, especially to lay down and move around. If they would have to be in the cargo area, then you should be able to get a nice big carrier like a large cat one or a small/medium dog one (like for 30 pound dogs).