If you can consider going Sony, not Kobo, then I can advise the following. A Sony PRS-T1 with the Japanese firmware can be used to buy and read Japanese ebooks overseas, at least here in New Zealand, but you need a Japanese credit card.
We installed the Japanese Sony Reader Software on English Windows 7 and used that to authenicate the ereader. Then my wife is able to buy nihongo ebooks from the Sony store in Japan, BUT only using a Japanese credit card. Once purchased we had no problems downloading the ebooks on the ereader in New Zealand.
Sony offer no guarantees or advice for any of this though. Their info says that the Sony Reader software for Windows requires Japanese Windows; but we have had no problems with it on English Windows 7.
Last edited by rjcroy; 07-27-2012 at 02:32 AM.