There's a huge North Korean community in Japan, which are a major source of funds to North Korea. Until North Korea confessed to abducting Japanese citizens c. 2002, there was even a ferry that traveled regularly between the two.
The main catch is that Japan's "North Koreans" may be internally registered as such, but they're actually descended from people who were in Japan before 1948 and for most part have never even been to North Korea. This is all further complicated by the fact that Japan doesn't actually recognize North Korea as a state and holds on to the fiction that South Korea is the sole legitimate country on the entire peninsula. Wikipedia has a capsule summary:
The main catch is that Japan's "North Koreans" may be internally registered as such, but they're actually descended from people who were in Japan before 1948 and for most part have never even been to North Korea. This is all further complicated by the fact that Japan doesn't actually recognize North Korea as a state and holds on to the fiction that South Korea is the sole legitimate country on the entire peninsula. Wikipedia has a capsule summary:
http://en.wikipedia.org/wiki/Chongryon