@v4r3l4 ,
1. I have found no articulations either by the US treasury or the IRS regarding non-taxability of already taxed monies being transferred abroad, except for interactions with directly or indirectly banned / notified entities/ persons. Thus my position that transfers to your spouse or to a joint bank account in Japan is valid. Your bank is the best source because for international transfers they often deal with corresponding banks in that country and their rules vary because of that arrangement. Also the receiving country may have limitations on incoming amounts ( depends on the currencies involved).
2. I had assumed ( may be in error ) that you are as US person ( probably H-1B or similar work visa or a Green Card whom plans to go back to your home country) and that your spouse is there in preparation for return to the home country. Thus I did not address the Estate Tax issue which has been very adequately addressed by @Opus 17 .
3. I have personally transferred more than US$200K to my wife's bank account ( she is the only holder of the account) for purchasing a property and with zero query either from the treasury or the IRS or the banks involved. Some of the amounts were below US$10,000, while others were multiples of US$10,000. Obviously the transferring bank in the USA wanted to know the purpose of the transfer , they surely raised the SARs but that is it.
I hope this has satisfied your query completely.
pk
