足利義満
Under the tributary system of China, monarchs of Korea and Vietnam sometimes called themselves "emperor" in their country. They introduced themselves as "king" for China and other countries (Emperor at home, king abroad). In Japan, Ashikaga Yoshimitsu a shogun was granted title of "king of Japan" for trade by the Ming's emperor. However, the shogun is a subject of the Japanese emperor. It was contrary to rules of tributary system, but Ming's emperor connived it for the purpose of suppressing the wokou.