Okimi
Ōkimi (, Ōkimi, Daiō) or Ame no shita Siroshimesu Ōkimi (, Chi Tenka Daiō) is the title of the head of the Yamato Kingship or the monarch title of Wakoku (Old Japan) from the Kofun period through the Asuka period in ancient Japan. Etymology 
The title "" (Ōkimi or Daiō), which is an honorific title for the head (king) of the Yamato Kingship, was established around the 5th century and was used until the 680s, when the compilation of the Asuka Kiyomihara Code started. There are several theories upon whether the title holder in the early period is a king of the unified kingship or not. Ōkimi in Japanese reading is created by adding the prefix "ō/oho," which indicates greatness and particular nobleness, to the title "kimi" (lord), which indicates a master or nobleman. Another theory states that "Ōkimi" is only an honorific form of "kimi," a title with Japanese origins, while Daiō is based on a king title which originated from China; the title of kango (Chinese word). There are many instances of the use of "", which is understood as a courtesy title of Emperor or royal family. Title of King of Japan in Chinese documents

King as a title in ancient China 
The kanji title "" (Ō, Wang) originally designated a Master of Chūgen (, Zhongyuan) in Inner China. In the Zhou dynasty period,  (Wang) was the title of the sole Son of Heaven who rules the Tianxia. However, some great powers in the region of the Yangtze civilization did not want to stand in subordinate positions of the nations of the Yellow River civilization in North China, such as Chu, Wu and Yue. Some of their monarchs titled themselves Wang. When China entered into the Warring States period, the monarchs of the great nations among the states of North China who were originally subjects of the Zhou King, but achieved territorial statehood, called themselves sole Wang of the Tianxia in place of the Zhou King. Thus, there were numerous claims to the throne in mainland China. Thereafter, Ying Zheng (), the King of Qin (Emperor Shi Huang), who unified China for the first time in 221 BC, adopted the title "Emperor" (, Huángdì) instead of title "King", which had been degraded. The King title Wang became the title granted to subjects of the Emperor, or that assigned to heads of neighboring states who recognized the authority of the Qin Emperor as Master of Tianxia, with a connotation of a subordinate rank. The latter usage was established thereafter. The monarch of Xiongnu stood on even ground with the Emperor of Qin, therefore his title was Chanyu, not Wang. Early title of King of Japan 
The first appearance of King title related to old Japan is  (Kan no Wi no Na no kokuō, King of Na in Wi of Han) engraved on the gold seal which was bestowed on the king of Nakoku by the emperor Guangwu of Han in 57 AD. The word Wakoku ō (King of Wa) appears in the article dated to the first year of Eisho (107 AD), in the record of Emperor An in the Book of the Later Han. The full title, as written in the record of emperor An, is: "Suishō, the king of Wa, and other". If "Wakoku ō" refers to the King of Wakoku as a head of the states union, other than a head of small regional state, this description shows the establishment of the Wakoku. In addition, Himiko (c. 180 AD–c. 247 AD) was authorised as the unified Queen of Wakoku (whose capital was Yamatai koku) by the Wei dynasty. There is a theory that the government that existed during Himiko's rule was an early form of the Yamato Kingship, though this has been disputed. Establishment of the Daiō (Great King) expression 
It has been theorized that Emperor Ingyō, who is identified with Sai/Sei (), one of the Five kings of Wa, is supposed to be the  (King) which is appeared in the inscription  on the  unearthed from the  in Chiba prefecture. If this is the case, then Ingyō may not be  (great king), but king. As for King Wakatakeru (Emperor Yūryaku), who is identified with King Bu (), there is the inscription  on an iron sword unearthed in the Inariyama Kofun in Saitama prefecture, as well as the inscription  on an iron sword unearthed in the Eta Funayama Kofun in Kumamoto prefecture. From these inscriptions, it is theorized that Yūryaku might have used the title "Chi Tenka Daiō" () inside Japan. It also suggests the title "Chi Tenka Daiō" was first used in the late 5th century. In Nihon Shoki, compiled in the Nara period, there are the scripts "" (Daiō, fūshi...) in the first Enthronement record of Ohosazaki no Sumeramikoto (Emperor Nintoku), but it is not certain that this Daiō had been used from the days of Emperor Nintoku, who ruled some 200 years before the compilation of the Nihon Shoki. However, the expression of Daiō appears in the Ōjin record, and after that, it appears in the Ingyō record, Yūryaku record, Kenzō record and Keitai record, among others. There is the inscription  (according to Toshio Fukuyama)  on the Suda Hachiman Shrine Mirror (Portrait of person Mirror), owned by , Wakayama prefecture, in which the words  and  appear. From this inscription, in the year Mizunoto Hitsuji (, Kibi)  when the mirror was made, the title Daiō is supposed to have been used. But there are various interpretations of what year this Mizunoto Hitsuji year was. In several theories, it is: 383, 443, 503, or 623 AD. Among these years, 443 (Emperor Ingyō) or 503 (Emperor Buretsu) are considered most likely. If it is 443, the expression Daiō was used in around the age of Ingyō, in the middle 5th century. However, the characters in the inscription are difficult to interpret. In addition, the content of the inscription itself has various interpretations. The exact years when the expression Daiō started to be used are unclear. In the Man'yōshū, the expression  is the most common, and 57 examples appear. Other expressions , , , and  also appear. However, all these words are read "Ōkimi" or "Ohokimi", and there are no examples that the single character  is read "Kimi". The word  is rarely used. There are only a few examples, such as the line  (Yasumishi shi waga ōkimi...) by Kakinomoto no Hitomaro. See also 
 Suishō
 Emperor of Japan
 Kofun period
 Asuka period
 Five kings of Wa

References 

Japanese monarchs
History of Nara Prefecture
Royal titles
Asuka period
Kofun period
Pages with unreviewed translations