Hello Mike (hh-60),
I have been a member of KAC for a loooong time and I remeber asking those similar questions about flying in Japan. Tama can give you the full scoop and now there is a guy named Aki, he just spent a lot of $$ to get his JP instrument commercial license, and is waiting for his golden phonecall; but in the meantime he's got to eat so he's at the club instructing- great guy by the way. Ask them for the latest info.
What I can offer you is the result of my research from a few years back. Major Japanese airlines(JAL and ANA) have a system- realize that all their subsidiaries (JEX, JTA, RAC, ANK, ANC, etc)follow their lead. So, for example, you, Japaense citizen, are recruited while "in" JP university, sent to flight training in the US, and then placed where they need you(737, 47, 67, 77, etc). US pilots with high "jet time," (key word) military or civilian, are contracted through various outsourcing agencies such as IASCO in California. For them to pool you requires again, high jet time- and they love heavy ex-military drivers. You are then contracted to fly as FO or CAP or FE and that is what you will fly for the contracted time. True, there are other companies that do similar outsourcing, but I only know of IASCO. Now remember Japanese airlines are still regulated/semi-subsidized by the government to a large extent and that's why they follow the system.
If you go for the small fry, i.e in Okinawa there are only 2 small air services- Ryukyu Air Commuter flying Dash 8's, and Air Dolphin, fying Cessnas and BN2's, there is the issue of your ifr/comm license. I met with the manager of air dolphin and he said that first, I, US civil pilot, need to transfer my ppl to JP ppl- that is not too hard, just re-take the written exam, physical and flight check. Then I must pass the JP ifr/comm exam and checkride. Japan Civil Aviation Bureau does NOT convert US ifr/comm/atp to JP standards no matter who you are. Ask Aki at the aeroclub, he is a Japanese citizen with US cfii and he had to pay to re-train to obtain his JP ifr/comm, also ask Tama. Short story long, they will hire their own before they hire you and me, unless your wife's family owns shares in an airline, and then perhaps after much prayer and fasting they might give you a thought- can you load baggage? Just kidding. So, with all that said, most folks who recommend gaining jet (key word is jet time) time in the US and then contracting yourself to one of the companies that outsourse airline pilots to Japan are also correct. I have met and spoken to about three american pilots at the airports in Osaka and Fukuoka and they were ex-military and contracted through IASCO and some other place in CA. Their advice was to get military jet time and after retirement seek the excitement of being contracted. They seemed to be ok with their experience, then again we only chatted briefly. Lastly, I also knew of a guy who flew helos for a Japanese corporation in Tokyo part-time. He was an instructor here long age and whenever they needed hime, they would call him and off he went. I believe he went back to the US after some time. So there may be a small crack into GA or corporate flying in Japan, but I do not know anything else about it.
As for me, my gig will be flying at the aeroclub as an instructor in the near future (a few years from now). I hope this gives some idea as to what is the real deal in Japan. I hope your training goes well, take care and fly safe.
Hernan