HT5557: iBooks: Frequently Asked Questions (FAQ) about iBooks featuresLearn about iBooks: Frequently Asked Questions (FAQ) about iBooks features
Currently Being ModeratedMay 12, 2013 2:16 PM (in response to Nekocha)
You can only buy content from your own country's store - so if you are in the US then you can only buy from the US store, to be able to buy from the Japanese store you will need a Japanese account with a valid Japanese billing address and be in Japan when buying from it.
You can try requesting that the Japanese ibooks that you want to buy be added to the US store, but ultimately it's the book publishers that will have to grant Apple a license to sell them there : http://www.apple.com/feedback/itunes.html
Currently Being ModeratedMay 12, 2013 2:50 PM (in response to Nekocha)
When your own country's ibookstore does not have what you want, the fix is to try the other stores which also provide free ereader apps for your device, such as Kindle, Nook, Kobo, Googlebooks, and Sony.