What is work-life balance like in academia in Japan? I am a current PhD student, still a couple years off from graduation. I'm still keeping my options open, but I've started to idly consider interesting places to do a postdoc.

Fit with a mentor and relevance of research is of course the most important thing, but the postdoc period is also a chance to live in cool places for a few years at a time. Work-life balance is also pretty important to me, though, and I have heard some crazy stories about work-life balance in general in Japan.

How is it in Japanese academia as a postdoc from the west? Does it depend on who you work for/what university you are in, or where you're from?

For reference, I did a bachelors in the US and a masters and (currently) PhD in Finland, where home life is highly respected and you're basically not expected to work on weekends/evenings unless you want to. 

Edit: If it's relevant, my field of study is genetics, but I mostly work on the computer and don't expect to have much to do with wet lab experiments in the future.
My personal experience is positive -- at least, in our institution, I don't really feel pressure from colleagues or management. However, I suspect it depends on a particular place. There are certain situations that I consider unavoidable, and thus I don't think people disrespect one's life-work balance, but unpleasant things happen.

For example, we might have grant deadlines or other paperwork in the middle of vacation, and of course, we are expected to get things done. Certain events like open campus, student competitons or entrance exams typically happen on weekends, and someone has to take care.

So, at least for me, most pressure comes from objective reality rather than someone's direct requests. When I have to work on a conference paper day and night to meet the deadline, that's for my own good, and I won't do myself a favor by missing it. The situation is more complicated in case of joint work when I can let down my colleagues, but perhaps Japan isn't special in such matters.

From the perspective of regulations, labor laws of course protect employees, and our administration actually asks us to take more vacation days to improve their stats, and they even offer additional vacations on top of what we have during the summer break. Your mileage may vary, but most professors around me don't push their students/postdocs too hard. I believe it might depend on the source of funding as well.