Chances are you will have big issues the Japanese government on that one, if you did not do your actual training in Japan. Example, there is a school in Bangkok, that does all of their nursing program in English, it is a four year degree program, the nurses from Japan that attended that school were not permitted to write the nursing exam in Japan as they did not do their training there.
The ones that returned are working in pharmaceutical sales, etc., but not as nurses there. The only option that you would have is the possibility of a US military base.
You can check with the equivalent of the Board of Nursing there, but you may be up against a brick wall. If the students that trained in Thailand, and were also Japanese citizens and with Japanese passports were not permitted to sit for the exam, I am not sure that you would be able to. Your US license is not good there, except if you work on a military base.
Hope that this helps..............