Seiwa was the fourth son of Emperor Montoku. His mother was Empress Dowager Fujiwara no Akirakeiko (明子), also called the Somedono empress (染殿后). Seiwa's mother was the daughter of Fujiwara no Yoshifusa (藤原良房), who was regent and great minister of the council of state.[4]
He was the younger half-brother of Imperial Prince Koretaka (惟喬親王; 844–897)
Before his ascension to the Chrysanthemum Throne, his personal name (his imina)[5] was Korehito (惟仁),[6] the first member of the Imperial house to be personally named "-hito" 仁. One meaning of the character 仁 is the Confucian concept of ren. Later it has been a tradition to name the personal name of all male members of the Imperial family this way.
He was also known as emperor as Mizunoo-no-mikado[4] or Minoo-tei.[7]
Originally under the guardianship of his maternal grandfather Fujiwara no Yoshifusa, he displaced Imperial Prince Koretaka (惟喬親王) as Crown Prince. Upon the death of his father in 858, Emperor Montoku, he became Emperor at the age of 9, but the real power was held by his grandfather, Yoshifusa.
7 October 858 (Ten'an 2, 27th day of the 8th month): In the 8th year of Montoku-tennō's reign (文徳天皇8年), the emperor died;[6] and the succession (senso) was received by his son. Shortly thereafter, Emperor Seiwa is said to have acceded to the throne (sokui).[8]
15 December 858 (Ten'an 2, 7th day of the 11th month): The emperor's official announcement of his enthronement at age 9 was accompanied by the appointment of his grandfather as regent (sesshō). This is the first time that this high honor has been accorded to a member of the Fujiwara family, and it is also the first example in Japan of the accession of an heir who is too young to be emperor. The proclamation of the beginning of Seiwa's reign was made at the Kotaijingu at Ise Province and at all the tombs of the imperial family.[9]
859 (Jōgan 1, 1st month): All New Year's festivities were suspended because of the period of national mourning for the death of Emperor Montoku.[10]
859 (Jōgan 1): Construction began on the Iwashimizu Shrine near Heian-kyō. This shrine honors Hachiman, the Shinto war god.[11]
869 (Jōgan 10): Yōzei was born, and he was named Seiwa's heir in the following year.[12]
876 (Jōgan 17, 11th month): In the 18th year of Seiwa-tennō's reign (清和天皇18年), the emperor ceded his throne to his five-year-old son, which meant that the young child received the succession (senso). Shortly thereafter, Emperor Yōzei formally acceded to the throne (sokui).[13]
878 (Gangyō 2): Seiwa became a Buddhist priest. His new priestly name was Soshin (素真).[11]
7 January 881 (Gangyō 4, 4th day of the 12th month): Former-Emperor Seiwa died at age 30.[14]
The actual site of Seiwa's grave is known.[1] The emperor is traditionally venerated at the misasagimemorialshrine in the Ukyō-ku ward of Kyoto. The Imperial Household Agency designates this location as Seiwa's mausoleum. It is formally named the Minooyama no Misasagi (清和天皇陵) or Seiwa Tennō Ryō.[15][16] From the site of his tomb the Emperor Seiwa is sometimes referred to as the Emperor Mizunoo (水尾帝, Mizunoo-tei).[17] The kami of Emperor Seiwa is venerated at the Seiwatennō-sha near the mausoleum.[18][19]
Kugyō (公卿) is a collective term for the very few most powerful men attached to the court of the Emperor of Japan in pre-Meiji eras.[20]
In general, this elite group included only three to four men at a time. These were hereditary courtiers whose experience and background would have brought them to the pinnacle of a life's career. During Seiwa's reign, this apex of the Daijō-kan included:
^Brown, pp. 264; prior to Emperor Jomei, the personal names of the emperors (their imina) were very long and people did not generally use them. The number of characters in each name diminished after Jomei's reign.
^Brown, pp. 286; Varley, p. 44; a distinct act of senso is unrecognized prior to Emperor Tenji; and all sovereigns except Jitō, Yōzei, Go-Toba, and Fushimi have senso and sokui in the same year until the reign of Emperor Go-Murakami.
^"Seiwa Tennō Ryō (清和天皇陵)". Nihon Rekishi Chimei Taikei (in Japanese). Tokyo: Shogakukan. 2012. Archived from the original on 2007-08-25. Retrieved 2012-05-18.
^"Seiwa Tennō". Nihon Daihyakka Zensho (Nipponika) (in Japanese). Tokyo: Shogakukan. 2012. Archived from the original on 2007-08-25. Retrieved 2012-05-18.
^"Seiwatennō-sha (清和天皇社)". Nihon Rekishi Chimei Taikei (in Japanese). Tokyo: Shogakukan. 2012. Archived from the original on 2007-08-25. Retrieved 2012-05-18.