I don't think the Japanese would be so careless.
They propably have high consequences for violation.
I don't know what country you live in where people don't check ID card.
Here in Germany whenever I buy alcohol, lottery ticket or enter a sex shop or the
adult department of a video rental store. It's strict here.
Except lame pornography, you can't buy pornography in the supermarket.
Selling pornography and material from the index (a banlist in Germany) outside of 18+ restricted areas is illegal in Germany. Advertizements, magazine and news reports about that material are also illegal. And the shopkeepers have to make sure no underaged kids get inside.
So whenever you want to buy pornography you have to go to a porno store or the 18+
department of the video rental store along with banned movies and games like Evil
Dead I & II, The Freddy Krueger Movies, Predator uncut, Scarface uncut,
SAW IV [the rest is outside the 18+ department in the horror department
accessable to everybody], Manhunt 1 & 2, The Punisher, the Austrian edition of
Fallout, the Austrian edition of Half Life
etc. Evil Dead 1[old] uncut is absolutely banned. Illegal anywhere in Germany.
What they don't ask me the ID card for anymore is beer. Since it's 16+ and I finally appear older.