>>208016
A lot of Japanese e-commerce sites require you to have a Japanese address in order to make an account. Other sites, such as Yahoo Auctions Japan, are even more strict in the sense they require you to have a Japanese phone number as well. There aren't any services that enable the latter, but there are plenty of proxy forwarding services that enable the former. Tenso and Blackship are the two I've used.
You sign up, verify your ID, and they give you a free Japanese address that you can ship items to domestically (it's usually some warehouse they own if you search on Google Maps). From there, you can consolidate your packages and have em shipped internationally for a fee. Once you have an address, you can then sign up for accounts on many Japanese e-commerce sites and pay with debit/credit.
With the Tatsumi Hiroshi tankobon, I made an account on suruga-ya and purchased a used copy from a seller there. With the other I just purchased it with my Amazon Japan account. The Yen has been experiencing extreme devaluation compared to the US dollar this past year so I didn't pay much for either. It's the shipping costs that'll get ya. Tenso and Blackship have their own subservices where they can purchase items for you (again, for a fee), but in the case of Tenso, viewing adult listings on Buyee is nearly impossible as many companies and sellers are afraid of violating obscenity laws. For Blackship, Japan Rabbit is their sister site and they've proven to be more forthcoming in that regard but, yeah.