Amazon.co.jp launched its Kindle store last month. When I logged into my US account today to see if the next Dresden Files book had come out yet, I saw a message telling me that I can consolidate my Japanese and US Kindle libraries.
Great news! You can now shop for Kindle titles at Amazon.co.jp. Consolidate your libraries and manage them from Amazon.co.jp. Change your preferred shopping site to the Amazon.co.jp Kindle Store to shop for Japanese titles in Yen.