In this page, you are using the word 'Sea of Japan'. But 'Sea of Japan' is misnomer. 

'Sea of Japan' is a unjust vestige of Japanese imperialism. This part of the sea has been called "East Sea" for more than 2000 years. The name 'Sea of Japan' was virtually non-existing till the recent past. By 19th century, even the maps produced by Japan referred to the sea between the two countries as the "Sea of Joseon(Korea)".

As you might know, at the turn of the 20th century, Korea fell prey to Japan's aggressive imperialism and got through painful colonial period. Japan's colonial rule was ended by World War II. However, some matters were yet to settled. The name of the sea between the two country is one of those.