couple good reads to give you a basic idea--http://www.lacba.org/Files/LAL/Vol27No9/2093.pdf
You might also contact the Japanese embassy at http://www.us.emb-japan.go.jp/english/html/ and ask to speak to someone in their legal section.
Best option is retain a family law attorney in our area who has experince enforcing US court orders in Japan.
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The prior attorney has laid out some good reads for you. For international child custody, it will be difficult because our laws and court decisions will not carry the same weight as it would between the states. You know that every country has their own laws and customs and what is acceptable here in the US will not be the same in the foreign country.
In specific, it really depends on the country where the ex has run off to. If it is indeed Japan, you will need to become familiar with the way that the Japanese courts work. The news articles you can find about such matters paint a very bleak picture for you if indeed this is the case. Your best option would be to find an attorney in the country where she has run off to and see how you can go about protecting your rights to the child using their system. The fact that you have a court order here in the US may help because it shows you are not just causing trouble, that you are indeed using the system to merely enforce your rights as you are granted by a court of law. How much influence will be up to the home court in that country.
Without knowing more information, it would be hard to say how you should go about proceeding on this matter. You can attempt to contact the State Department and see if they can refer you to a particular help desk or body that can provide you with further assistance.
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