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!
If you can not find a store which ships direct to you. Or to combine shipment which you buy on different store. You can arrange a forwarding service. Rakuten introduce two forwarding company and flow as follows.
To find products efficiently first I'll recommend you to select your preferred language, currency and shipping country. And then narrowing down the categories. If you fail to select the shipping country search will include domestic only store and will be hard to reach overseas shipping store. If you are going to arrange forwarding services. Choose "Japan or Use Forwarding service" on the Shipping county the search will go through all the products on Rakuten Global.
To help you to buy stuff direct from Japan through Japan's largest and well known online shop Rakuten and amazon.jp