If you are asking geographically, the country opposite of Japan is South and North Korea.
japan
Japan is a large country in the south pacific
Okinawa is an Island south of Japan and today it is part of the country of Japan.
South Korea
Japan is an island nation without any borders.
South Korea
look on bing
Korea (both North and South) is between China and Japan.
Japan, Taiwan, Singapore, and South Korea
South Korea and Japan
Japan is an archipelago consisting of four major islands on the Eastern edge of Asia. Its closest neighboring country is Russia.