Can I buy an unlocked iPhone in Japan?
It is possible to buy a unlocked iPhone at any apple-store in japan, but there are the following issues:


LTE Freqency Band does not match (Japan 2,1 GHz / Brazil 2.6 GHz). That means, LTE will not work. You will need the model A1778 and in Japan you can only buy the model A1779: http://www.apple.com/iphone/LTE/
You can not claim any warranty replacements outside of japan