There’s been a little discussion on the Kumamoto-i mailing list about how to get or transfer a driver’s license.
https://groups.yahoo.com/neo/groups/kumamoto-i/conversations/messages/12801 https://groups.yahoo.com/neo/groups/kumamoto-i/conversations/messages/12802 https://groups.yahoo.com/neo/groups/kumamoto-i/conversations/messages/12803
If you search the Kumamoto-i archives, you can find more information about this topic.