Empress of Japan

Japanese empresses or Empress of Japan means a . The term also mean the wife of the Emperor, or .
The wife of Naruhito is Empress Masako. She became the current Empress of Japan when her husband accepted his role as emperor.
Empresses regnant.
There were eight female monarchs. In other words, there were six female emperors including two who reigned twice. 
Empresses consort.
The wife of an Japanese emperor is called empress in English, but her title in Japanese is a little different.
"Kōgō" is the title of a non-reigning empress consort. The title, still in use, is generally conferred on an emperor's wife who had given birth to the heir to the throne. The title was first awarded posthumously in 806 to the late mother of Emperor Heizei.
"Chūgū" was a term which evolved during the Heian period; and it came to be understood as the title of the empress. For a time, "chūgū" replaced "kōgō"; and then the titles became interchangeable.
The numbers of "kōgō" varied, but there was only one "Chūgū" at a time.
The title "kōtaigō" was given to the wife of an ex-emperor; and the title "tai-kōtaigō" came to be used by a dowager empress.