In the Japanese employment system, a key task is to build connections. While this can be said to be valuable in all contexts, it is invaluable in the Japanese context. You will not (unless you are already well-renowned and hired by a fan) find a good job in Japan without first developing connections. The good news is that , in my experience, most of the academics in Japan are quite good sports.
Over the weekend, I participated in two conferences. In the former, I presented a paper in my specialization in Japanese. In the latter, I merely attended as a member. Through both, I was able to talk to several professors at the 総宴会 and 二次会. Basically, if you want to connect with Japanese professors, you need to go out drinking with them. The academic world in Japan is still largely a playground for old men who enjoy drinking (and possibly smoking). But really without doing so, you will not succeed in building connections.
Moreover, you should join academic societies and let your face be seen around and about the town.