It is an absolute mistake to hear just one side of the story and to blindly follow. If we leave these kinds of things alone, it causes serious problems that disturb the order of international society.
For your reference, Dorling & Kindersley(https://www.dk.com), one of biggest textbook publishers,
worldatlas.com, one of prominent online map provider, and one of the biggest mapmakers, National Geographic promised us that
they would now use the name 'East Sea.' In addition, these websites are already using the name, 'East Sea' on their website after we pointed out the error.
http://whyeastsea.prkorea.com/our-effort
Most of all, the U.S. state of Virginia has revised the guidelines for history and social science education in line with a newly enacted law that requires textbooks to use the Korean name "East Sea" alongside the Japanese name "Sea of Japan"
for the body of water between the two countries on 2017.
As a member of the Voluntary Agency Network of Korea . I urge you to use 'East Sea' to describe the body of water in question or to use both Korean and Japanese designation simultaneously (e.g. 'East Sea/Sea of Japan') in all of your contents and maps.