Just so you know, I wasn’t asked nor paid to review this site (though that would be nice, wouldn’t it?), but I’m sharing it with you because I think some of you might find it useful. Now, the site has two language versions: Japanese and English. Most of the products I have seen on the Japanese version are available on the English version, though there were a few discrepancies here and there. (And, the English translation is done by a computer, so you’ll notice some of the wording sounds a bit funny). However, if you try to check out while using the English version, you will be asked to pay by credit card, as this is the only option for payment on the English version of the site. Reason being, probably because they ship internationally. On the other hand, the Japanese version of the site allows you to order by credit card, convenience store pay, postal transfer, and cash on delivery.
So what to do?
Shop in English (if you so prefer, or dare to shop in Japanese with Google translate or Rikaichan (Firefox) or Rikaikun (Chrome)) and when you know what item(s) you want to buy, click on “JAPANESE SITE PAGE” in the wide box just under the short product description. This will take you to the Japanese page for the same item, at which point you can “add to cart” by clicking the large yellow button on the right (商品を購入する).
Then, you can go back to the English site to do more shopping, repeat the above process, and your cart should save all the items (so long as you don’t leave your computer for a long time). Once you’re ready to checkout, just click on the large yellow button at the top or bottom of your cart, which says: 購入／お支払い手続きへ進む (こうにゅう／おしはらいてつづきへすすむ; kounyuu/ oshiharai tetsuzuki e susumu; purchase/ continue to pay).
You will need to make an account (like most websites it seems). So, assuming this is your first time, you’ll make sure 初めて (はじめて, hajimete, first time) is selected, enter your email address in the top box, and press the continue button at the bottom.
Now, the rest requires filling in your personal information (in Japanese), followed by choosing your desired delivery day and time, and choice of payment. For some help with these, remember Google translate, an electronic dictionary (on your computer or online) and browser tools are very helpful (see this post for more ideas). Then just choose the appropriate info, confirm, and wait for your confirmation email. A few helpful words to know when ordering online:
レジ (reji - register) - usually on the button you click from the shopping cart to place an order
進む (すすむ, susumu - advance, go, continue) - often with "reji". レジへ進む or レジに進む, but sometimes not.
送料 (そうりょう, souryo - shipping) - the amount of shipping costs
合計 (ごうけい, goukei - total) - the total price, usually including shipping
配送日 (はいそうにち, haisou nichi - delivery day) - you can often choose the delivery day (or leave at the default if it doesn't matter when)
配送時間帯 (はいそうじかんたい, haisou jikantai - delivery time) - specify a delivery time (or leave it at the default if it doesn't matter when)
クレジットカード (kurejito kaado - credit card) - specify credit card information here when choosing payment options
代金引換 or 代金引替 (だいきんひきかえ, daikin hikikae - cash on delivery) - choose this option for C.O.D.
振り込み (ふりこみ, furikomi - bank transfer) - choose this for a bank transfer
コンビニ (konbini - convenience store) - choose this to pay at a convenience store
Of course, this isn't Amazon.jp, but may have some other/different options for those of you living in Japan (or even elsewhere as they ship internationally), and also allows you the opportunity to read a bit more in English without using Google translate all the time.