Japan is a giant market for bitcoin because its population and because it´s a technology friendly country. As a example you can see some concerts in youtube recorded with smartphones that sound better than profesional recordings. Furthermore there is another little detail, the bitcon creator´s name is Satoshi Nakamoto, it sounds like a Japanese name, a small detail that, through identification, can create more sympathy for bitcoin in the country.
The point of Satoshi Nakamoto is pretty decent and also Japanese government just recently announced bitcoin as legal in Japan so the investors from Japan are being inetersted in bitcoins which is attracting more money in bitcoins and driving the price pretty high in $1800s in some japanese exchanges yesterday.