The shipping cost is quite different between amazon global and Rakuten Global. amazon affiliates with private carrier but most of the Rakuten store use Japan Post for shipping outside Japan. If you find an item you want check the total cost on the other. The best way is to ask the total cost before the order. But if you want to know the rough cost here below are the official shipping rates. (it's the rough caluculation so some items may hav a specail packing)
Enjoy your shopping with saving money!
To help you to buy stuff direct from Japan through Japan's largest and well known online shop Rakuten and amazon.jp