I found that the sea between the Korean peninsula and Japan was labelled as the ¡°Sea of Japan¡± instead of the ¡°East Sea¡± in your title.
Unfortunately, this is an error. The name ¡°Sea of Japan¡± was first used during the period of Japanese Imperialism. But the sea had been called the ¡°East Sea¡± for more than 2,000 years originally.
This fact is based on various historical evidence. The correct indication of this sea is not the Sea of Japan.
Therefore, The sea ¡° between Korea and Japan should be correctly expressed as the ¡°East Sea¡±.