Finally decided to start a post. I don' t know how many people are interested in reading about post-doctoral life in Japan, but hopefully this will prove informative.

There are a number of ways of becoming a post-doc (ポスドック) in Japan, but the most straight forward method is getting yourself a fellowship. The big fellowship in Japan is the Japan Society of the Promotion of Science (JSPS) Long-term postdoctoral fellowship (日本学術振興会外国人特別研究員), which is very competitive and difficult to get. If you apply directly through a Japanese host, I think the applicant to award ratio is about 100 to 1, however if you try to get a nomination through an agency in your home country, the chances are better. Of course you'll need to find a host researcher in Japan to get the ball rolling as well as a PhD. If you don't have a PhD, there are a number of scholarships such as the Crown Prince Akihito Scholarship (if you are a University of Hawaii graduate student) as well as the Monbukagakusho Graduate Fellowship (MEXT; 文部科学省) that will fund your graduate studies in Japan.