Sorry to say this but the situation is dreadful at the moment. I've literally booked hundreds of award tickets between US and Japan in the past with no problem, but availability has crashed over the last several months. The only reliable option right now is UA, but that's 200k miles for J one way.... which is on a equivalent basis more than you would pay for a cash ticket. If I were in your shoes, I would grab the one way to Japan, and then for the return a) hope something opens up for the way back, b) bite the bullet and come back in Y, or c) or for the return buy a RT J originating in Japan for $4-5k and then plan to come back to Japan within a year.