Announcing GitHub Japan
github.com
github.com
Additionally, after you have a subsidiary, you have a very straightforward way (intra-company transfer) to get e.g. US employees work-capable Japanese visas in a fashion which is very not straightforward if you lack a Japanese entity. (If you have e.g. an engineer who you want to place in Tokyo who doesn't come with e.g. Japanese citizenship, permanent residence, or a spousal/parent visa, then getting them an engineering visa requires roughly three bullet points, one of which is a contract with a Japanese organization to do engineering work. It's a black letter law requirement and you will not be successful in getting an engineering status of residence without it.)
n.b. Not a lawyer, not an accountant, but if anyone from the US is ever getting an office set up here drop me a line and I'll give you the quick rundown.
Lots of people in Japan, even techies, have less than stellar English skills. There are also a lot of companies here that are still in the dark-ages when it comes to technology (e.g. I worked at a company that tried CVS in 2009 before I joined but didn't see the point of version control)
Sales / Support staff fluent in Japanese will help a lot I think.
Japan has 130 million people. I think there is probably lots of room for Expansion for github. Having a Japanese sub also makes taking payments easier, I am sure there are other legal / administrative reasons.
The Ruby VM really need some spanking.