I'm spending a day in Tokyo, and expect to have pistachios with me, so I had to find out if Japan allows them to transit.

Most types of nuts (with the exception of walnuts, which are prohibited) may be brought into Japan, particularly if they are salted, dried, or roasted.

[ Consulate General of Japan ]

I'm sure this will come up on Jeopardy in the next week, or be a vital fact that a friend needs to know.

Update: The prohibition of Walnuts is not due to a dislike of Walnuts, or an aversion to Walnuts, but an attempt to keep pests out of Japanese crops.