[dirtyroboto]

Kungmartin, I spent most of my life in and around London and some time in NYC and Florida. I was in the music business for a while, you can guess what that means right!
It means I have seen it all when it comes to drugs and drink.

In Japan you can't buy Rizla. (To locals, I know that, don't flame).
But the main factors that others have pointed out is the social stigma.

In the west you will get laughed at by your spliff smoking parents, sisters and brothers if you don't suck the weed. Your friends won't talk to you and your Boss may fire you for not having a spare paper.
Kids in the west now use drugs as fashion. It's more down to what you can score then what you wear.

In Japan, life is still going on as usual. There has been an increase in immigrants who take drugs and by association introduce drugs to Japanese. There are Japanese who try to smuggle drugs into Japan for an easy buck.
For the most part, and I mean 99% the Japanese are not interested in that part of western culture.

And it is this point. That Japan has by and large protected it's people and their welfare that is the reason you won't find a drug culture here.
While western governments have failed and Islamic states have used religious and barbaric deterants. Japan has helped it's people avoid the onslaught of drug culture.

So, if you are a tourist in Japan I guess you could find a smoke quite easily. If you don't mind hanging around in the same place as people who will rob you or spike your drinks, that is. When I say Japan I mean Tokyo, oh! when I say Tokyo I mean a small part of Tokyo.