Hello Sai

To do an MS or MD you need  Bachelors degree or an international equivalent and pass GRE or any  graduate entry test score. You will have to take Japanese-Language Proficiency Test (JLPT) (https://www.findamasters.com/advice/entry-tests/masters-japanese-language-tests.aspx) . You will need to fill the application form, normally available online or as a downloadable document, personal statement, sometimes called the “academic essay”, Bachelor diploma (if you have already graduated) and transcripts, References/letters of recommendation (most often two), English-proficiency test scores and certificates (and Japanese equivalent if required) and Application fee certificate or receipt. You will need a visa.

There are a few things you need to know

Your first task will be to clear the Japanese Language Proficiency Test depending  on  your purpose.Most medical text books will be in Japanese. If you plan to stay there it will be all the more difficult as most Japanese people prefer Japanese doctors over foreign doctors. However Japan has seven of its universities in the top 50 in Asia (two of them in the top 100 in the world.  it is very hard to see Indians / Other foreign nationals who studied in Japan and have taken up Top position in Japanese Corporates.