Legally uncensored porn cannot be sold in Japan, the law does now allow for display of the genitals.
The uncensored studios get around it by filming outside Japan or pretending that they only sell outside Japan, even though their websites are in Japanese etc.
Japan is often like that. Like for example gambling is illegal, so pachinko parlors let you win non-cash prizes which is legal. Then you go around the corner and there is a little shop where you can sell your prizes for money, and the shop sells them back to the pachinko parlor. It's no secret, everyone understands it, but the police don't care and politicians aren't interested in shutting down a really popular passtime for millions.