patio11 on HN (Patrick McKenzie) [0], who works for Stripe in Japan, has many things to say about working in Japan, not all of them good. Mainly (depending on the company, and whether it's American with a Japanese branch versus Japanese-founded), there is a level of business bureaucracy that isn't present in the US, as well as startup funding being nearly non-existent. On the social side, it is very difficult to assimilate as a Japanese citizen, as most Japanese people will only consider you truly Japanese if you were ethnically Japanese.

[0] https://news.ycombinator.com/user?id=patio11