Ziggy,
We do not have the answer to your question. You need to talk to mechanical engineers in Japan and the people who hire mechanical engineers in Japan.
Some other good people to talk to are professors who teach mechanical engineering at universities in Japan,
I think that only these people can answer your question.
I did a quick Google search. You need to contact professors at these universities and ask them your question.
6 Universities in Japan offering Mechanical Engineering degrees and courses. Plan your studies abroad now.
nturanking.lis.ntu.edu.tw
Tokyo University of Science official website. Information about Department of Mechanical Engineering at TUS.
www.tus.ac.jp
Mechanical Engineering degrees at universities and colleges in Japan - Find 6 Bachelor's Degrees in Mechanical Engineering to study abroad.
Also, universities usually have a Career Counseling and Hiring Office. Engineering colleges in Japan should have such an office. Contact all of them in Japan. Of course hiring offices at engineering colleges in Japan know which are the good engineering companies in Japan. Talk to them.
Then there are the companies who hire mechanical engineers. What are the top companies in Japan that who hire mechanical engineers? Find out. Communicate with them. Ask them your question.
Is there some sort of international fellowship and member organization of mechanical engineers? Is there one in Japan? Does such an international organization have a group in Japan? Join these organizations. Get to know these people. There may be such members in your coumtry that you can talk to.
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Only after you have talked to these people will you have your answer. You may need to visit Japan on vacation just to talk to these people.
Do not make your decision until you have talked to all of these people.
Choosing a major and a career takes a lot of hard work. Get out there and do all of this hard work.