The Japanese average IQ has been estimated to be 104. It is slightly lower than the Chinese and Korean averages.
The the highest IQ, in prefecture Akita, had 107 while the one with the lowest (Okinawa) had 96. This is surprising in that it challenges the much-touted homogeneity of Japanese people.
Further, people living in the northern part of Japan are taller, more intelligent and less crime prone. They divorce less often, have lower fertility.
Skin whiteness is positively correlated with latitude and also with IQ, and their correlation is almost the same.
And we can calculate that 1 IQ point raises average income by 2.5%.

Kenya Kura; Japanese north–south gradient in IQ predicts differences in stature, skin color, income, and homicide rate; Volume 41, Issue 5, September–October 2013, Pages 512–516