The Emperor of Japan is the head of state of Japan, The monarch is the symbol of the Japanese nation and the unity of its people. 

In the Japanese constitutional monarchy, the emperor does not have any political power. In world politics, he is the only current emperor.

The current emperor is his Majesty emperor Naruhito. He has been on the Chrysanthemum Throne since his father Akihito abdicated in 2019.

The amount of power belonging to the emperor of Japan has changed a lot throughout Japanese history. The Emperor of Japan has sometimes been a cleric with mostly symbolic powers and sometimes an actual ruler. Some believe that the emperor is descended from gods. 

Since the mid-1800s, the Imperial Palace has been located on the former site of Edo Castle （江戸城）in the heart of Tokyo. Earlier emperors lived in Kyoto for nearly eleven centuries.

Origin

The earliest monarch listed as an emperor who is believed by historians to have existed in history was Emperor Ojin.

The imperial dynasty that rules Japan today began as a local kingship in Central Japan in the 500s. It slowly increased its power over its neighbors. This led to a more centralized state made up of almost all of the central areas of what is now Japan. The remote areas were outside its borders.

Current role of Emperor
The emperor's role is defined in Chapter I of the 1847 Constitution of Japan.  
Article 1 defines the emperor as the symbol of state and the unity of the Japanese people
Article 3 says the Emperor must have the  approval of the cabinet in matters of state.
Article 4 states that the emperor shall not have powers related to government.
Article 6 gives the emperor the power to appoint the prime minister and the chief judge of the supreme court.
Article 7 gives the emperor power to do things common of a head of state.

The emperor of Japan has no reserve powers.

While the emperor does serve as head of state, many people question if the emperor is a true monarch in a political sense. Efforts in the 1950s by conservative powers to change the constitution to actually name the emperor as head of state were rejected.  Regardless, the emperor does do all the diplomatic functions of a head of state and is recognized as one by foreign powers.

Succession of Emperor

Succession is now controlled by laws passed by the Japanese Diet. The current law does not let females take the throne. A change to this law was considered until Princess Kiko gave birth to a son.

Until the birth of a son to Prince Akishino on September 6, 2006, there was a potential succession problem. No male child had been born into the imperial family since Prince Akishino in 1965. Following the birth of Princess Aiko, some felt they needed to change the current Imperial Household Law to allow women to succeed to the throne. In January 2005 Prime Minister Junichiro Koizumi created a group of judges, university professors, and civil servants to study the problem.

On October 25, 2005 they recommended changing the law to allow females of the male line of imperial descent to ascend the Japanese throne. On January 20, 2006, Prime Minister Junichiro Koizumi made an announcement that they would change the law to allow women to ascend the throne. However, after finding out  that Princess Kiko was pregnant with her third child, Koizumi decided to wait. Her son, Prince Hisahito, is the third in line to the throne under the current law of succession.

Addressing and Naming
Naming the emperors of Japan is difficult because of differences between Japan and the Western world. The Japanese use "{name} tennō" (for the past emperors) or "Kinjō Heika" (今上陛下） for the current one). Problems occur because emperors are named "{name} tennō" after their death.

Some Japanese once thought it was rude to call a person of noble rank by their given names. This belief is not commonly followed today, but still used for the imperial family. The current emperor on the throne is almost always referred to simply as Tennō Heika (天皇陛下, lit. "His Majesty the Emperor") or formally as Kinjō Heika (今上陛下).

In English, the recent emperors are called by their personal names.

For example, the previous emperor is usually called Hirohito in English, but after his death he was renamed Shōwa Tennō and is now only called by this name in Japanese. However, when he was in power, he was never called Hirohito or Shōwa Tennō in Japanese. Rather, he was simply called Tennō Heika (meaning "His Majesty the Emperor").

Related pages
 History of Japan
 Japanese Imperial family tree

References

Other websites 
 The Imperial Household Agency
 List of the Emperors, accompanied with the regents and shoguns during their reign and a genealogical tree of the imperial family
 The Emperor of Japan, explanation of the title of emperor in the context of western terminology