The five kings of Wa (倭の五王)
The five kings of Wa refer to San (讃), Chin (珍), Sai (済), Ko (興) and Bu (武) who paid tribute to the Eastern Jin and Song (Southern Dynasty) in the period of the Northern and Southern Dynasties (China) in 5th century and received sakuho (homage by Chinese emperors) as 'King of Wa'.
They paid tribute at least nine times between 413 and 478. Following is the chronological table.
Emperors and the five kings of Wa
One theory assumes that, from imperial lineages in "Nihonshoki" (Chronicles of Japan) and other sources, 'San' was Emperor Richu, 'Chin' Emperor Hanzei, 'Sai' Emperor Ingyo, 'Ko' Emperor Anko and 'Bu' Emperor Yuryaku. Researchers have nearly reached consensus on the identification of 'Sai', 'Ko' and 'Bu' in the above theory, but 'San' and 'Chin' are yet to be confirmed due to discrepancy between the traditions written in Sungshu (Book of the Sung dynasty) and Kiki (Kojiki [Record of Ancient Matter] and Nihonshoki). Other prevailing theories include the one which says 'San' is Emperor Nintoku and 'Chin' is Emperor Hanzei and another one which says 'San' is Emperor Ojin and 'Chin' is Emperor Nintoku. According to a theory which identifies 'Bu' as Emperor Yuryaku, the Chinese character '武' can be read 'Bu' as well as 'Takeru' which corresponds to a part of the king's name inscribed on iron swords (Wakatakeru no Okimi [the Great King Wakatakeru] in Inariyama-kofun Tumulus, and the Wa□□□ru no Okimi in Eta Funayama Tumulus) and this king has been identified as Emperor Yuryaku, whose real name and his Japanese-style posthumous name (Ohatsuse no Wakatakeru no Mikoto in "Nihonshoki" and Ohatsusewakatakeru no mikoto/Ohatsuse no miko in "Kojiki") commonly include 'Takeru'. If this theory can be applied to other kings, '讃' or 'Homu' may be for Emperor Ojin whose real name is Homutawake, '珍' or 'Mizu' for Emperor Hanzei (Mizuhawake), '済' or 'Tsu', for Emperor Ingyo (Woasazumawakugonosukune), and '興' for Emperor Anko (Anaho) because '興' means excitement and 'Ana' is a note of admiration. But none of the theories is decisive and the identities of the five kings remain uncertain.
There even exists a theory which says that 'the five kings of Wa' are not among the kings of Yamato Dynasty because the envoys of 'the five kings of Wa' are not recorded in "Kojiki" or "Nihonshoki" and also because none of the kings of Yamato Dynasty had a Chinese-style name with one Chinese character, such as 讃, 珍, 済, 興 and 武.
Kyushu dynasty theory separates Waobu (Japanese king 'Bu') from Wakatakeru no Okimi on the inscription or from Emperor Yuryaku or other kings of Yamato Dynasty, but instead, thinks that 'Bu' was the successor of Yamatai Kingdom who subordinated them. This theory identifies Waobu with Yamatotakeru no sumeramikoto who appears in Fudoki (description of regional climate, culture, etc.).
The purpose of dispatching envoys and presenting tribute seems to have been to develop a political diplomacy with the other powers in the mid-western part of Japanese archipelago and Korean peninsula with the help of the prestige of the Southern Dynasty, as well as absorbing the civilization and caulture of the Chinese continent.
Correspondence relationship with the chronology in "Kiki"(the Kojiki and Nihonshoki)
Alothough "Kojiki" does not contain a chronology, it tells, as an annotation, the Oriental zodiac of the year when some of the emperors died. One of the theories identifies the five kings of Wa from the Oriental zodiac of the years of their death. Following is the years of death of related Emperors written in "Kojiki".
15th Emperor Ojin, Kinoe-Uma (394)
16th Emperor Nintoku, Hinoto-U (427)
17th Emperor Richu, Mizunoe-Saru (432)
18th Emperor Hanzei, Hinoto-Ushi (437)
19th Emperor Ingyo, Kinoe-Uma (454)
21st Emperor Yuryaku, Tsuchinoto-Mi (489)
26th Emperor Keitai, Hinoto-Hitsuji (527)
Assuming that the Oriental zodiac recorded in "Kojiki" is correct, 'San'=Nintoku, 'Chin'=Hanzei, 'Sai'=Ingyo, "Ko"=Anko, and "Bu"=Yuryaku. However, there is an inconsistent data with the description in "Sung Shu" (Book of the Sung dynasty). That is the following description in Wakoku Den (Story of Japan) "Sung Shu".
Sai dies, his younger brother Chin accedes to the throne and his envoys present tributes..'
In 436, Sai died and his younger brother Chin acceded to the throne. His envoys presented tributes.
(Wakoku Den "Sung Shu")
This description recognizes Chin as Sai's younger brother.
Hanzei, who died in 437 according to "Kojiki", was the father of Nintoku as long as referring to "Kiki". If San were Nintoku and Chin were Hanzei, it would be inconsistent with the description in Wakoku Den "Sung Shu" which recognizes Chin as the younger brother of San. Hanzei should have been the younger brother of Richu. It may be possible to conjecture the five kings of Wa from the Oriental zodiac of the years they died recorded in "Kojiki", except for this inconsistency.
On the other hand, the chronology in "Nihonshoki" writes there were only three Emperors between 413 and 479: Ingyo, Anko and Yuryaku. But Chinese history books tell there were five. While Chinese history books say that envoys were sent by San in 421, Chin in 436 and Sai in 443, we can find, in "Nihonshoki", only one Emperor whose reign falls into this period which is Ingyo who was in power from 411 to 453. A correspondence relationship cannot be confirmed between the chronology in Chinese history books and that in "Nihonshoki".
There is no clear mention about the envoys of the five kings of Wa in "Kojiki"and "Nihonshoki" in the first place. In agreement with the criticism on "Kiki"'s credibility as historical material and from the fact that the chronology before Emperor Keitai is far from truth, and that it is hard to believe that the Imperial family kept written records on a steady basis, some people strongly deny the meaning of the attempt to presume the five kings of Wa from the Oriental zodiac and the genealogy in "Kiki".