I'd check out 東京Node学園祭, the main node conference in Japan, for an idea of the kind of companies that use it.
React has been getting a fair amount of attention within the developer communities here over the last year or so, and I know some companies using it.
Rather than trying to pick up a new technology, I think your time would probably be better served increasing your public presence as a developer. If you can demonstrate that you're a really great developer, companies will hire you regardless of what technology you know.
Also, the reason why you see Rails mentioned more throughout this site is that's the community I happen to be most involved with. While it has been booming, I think there is demand for developers with pretty much any skill set here.