that sea is NOT Japen Sea.

Japen has been made most of maps which has the sea between Korea and Japen as Japen sea.

Actually, that sea is owned by Korea , not Japen.

In that area. Japenese have no rights to get there.

In the actual map, they made Japenese sea, but the actual name is Korea sea or east sea..

Answer

At the moment it is known as the Sea of Japan, but in my latest atlas it is named as the Sea of Japan (East Sea). This is because of a official dispute between Japan and North and South Korea over the name, which is currently in the hands of the United Nations.

Japan wants it to stay as the Sea of Japan, while the Koreans want the old name of the East Sea restored.