FANZA's official answer is no: its services are intended for Japan and cannot be used from outside Japan. The overseas-use help page says this in both Japanese and English.
The confusion starts when another official page says some foreign-issued cards are accepted. Card compatibility and overseas service availability answer different questions. An accepted card brand does not turn a Japan-only service into an internationally supported one.
What the foreign-card page actually says
FANZA's foreign-issued card FAQ lists Visa, JCB and Diners, with narrower rules for some services. In particular, Books, Books Unlimited and Doujin list only JCB and Diners among those foreign-issued cards.
Meanwhile, the service-by-service payment table says overseas customers cannot pay by credit card. It also shows that different FANZA services offer different payment methods.
These pages do not establish a reliable checkout route for someone abroad. They also do not define every account or residency condition for a foreign visitor physically in Japan. If you are visiting, check the exact service and your actual checkout eligibility; do not infer approval from a brand logo alone.
In Japan but still getting a region error?
For someone physically in Japan, the official regional-error instructions point to the connection: an overseas provider, VPN, security software's VPN, proxy or unsupported browser can be involved. The published remedy is a normal domestic-provider connection with those routing features disabled.
This can explain why sitting in a Tokyo hotel does not automatically produce the expected result. Your physical location and the network route used by your device are not necessarily the same.
Check the connection you already have and the service's requirements. A region error is not a reason to buy extra store credit on the assumption that the money will solve access. Payment and access remain separate.
Buying during a trip does not promise access after it
Before paying, decide where you expect to use the purchase. Is it something you want on your laptop in Japan, or something you intend to read after returning home?
FANZA's overseas policy does not provide a guarantee of continued service abroad. That is not the same as claiming every downloaded file stops opening at the airport. The particular work's file format, viewer and authentication requirements matter, and a general platform article cannot certify them all.
For a purchase you already own, keep its receipt and product code and identify the precise problem: sign-in, download, reader launch or playback. Those details are useful to support. “The site doesn't work” leaves too many possibilities.
Find an authorized edition that fits your location
Use the creator or publisher's own links to look for another authorized release. Match the exact title, language and edition; the same cover does not necessarily mean the same version. If an English DLsite edition exists, check its translation and format before purchasing.
Do not assume another store carries the title, or that a successful homepage visit guarantees your country's purchase eligibility. Establish those points before loading a wallet or buying a second copy.