As the Heian period (794–1185) was coming to an end, two rival clans battled for dominance over Japan. Initially successful, the Taira Clan insinuated itself in Kyoto. Taira no Kiyomori moved to have his young grandson made emperor of Japan. Alarmed at growing Taira power, retired Emperor Go-Shirakawa called for the overthrow of the Taira. The Minamoto Clan had been defeated by the Taira earlier and the surviving Minamoto leaders wanted revenge. They saw their opportunity in 1180 with retired Emperor Go-Shirakawa’s opposition to the Taira Clan. In 1180, Taira no Kiyomori made his two-year-old grandson emperor (Antoku). Meanwhile, Go-Shirakawa’s son Prince Mochihito aligned himself with the Minamoto Clan who supported his claim to the Imperial Throne.
The Genpei War between the Minamoto and Taira Clans lasted five years. Prince Mochihito was killed at the outset (June 1180, after the Taira victory at the First Battle of Uji). Taira no Kiyomori died in 1181. The Battle of Kurikara, in which badly outnumbered Minamoto forces defeated the Taira, marked the turning point of the war. In 1183, Emperor Antoku and the Taira fled the capital, taking the regalia with them. Retired Emperor Go-Shirakawa then made his own grandson (Go-Toba) emperor. During the last two years of the war, there were two rival emperors. Emperor Go-Toba’s accession was the first in which the regalia was not ritually handed over to the new sovereign.
The two emperors were children (Antoku born in 1178 and Go-Toba born in 1180), basically the pawns of powerful clan leaders or court nobles. In early 1185, the Taira Clan were on the verge of losing the war. On 25 April 1185, Minamoto and Taira forces clashed at Dan-no-ura in the Shimonoseki Strait. Minamoto forces were led by Minamoto no Yoshitsune (1159–1189), Yoritomo’s half-brother. The Taira forces had two main commanders: Munemori (1147–1185) and Tomomori (1152–1185). In addition, nearly all of the key Taira leaders were present at this battle. Emperor Antoku was on board a Taira ship with his grandmother (Kiyomori’s widow) the Nun of the Second Rank.
When the battle was lost and the Taira were decisively defeated, a mass suicide began. Taira leaders jumped into the water, their armor pulling them to the bottom of the sea. The child Emperor Antoku was in the arms of his grandmother. She told the child sovereign “beneath the waves lies our capital.” Then, with the emperor in her arms, she jumped into the sea. She also took the sacred sword (part of the Japanese regalia) with her. The jewel and mirror (the other two items of the regalia) were also thrown into the sea. These latter two items were recovered. According to the Tale of the Heike, the sword (Kusanagi) was lost, making the present sword a replica.
Emperor Antoku is indeed a tragic figure: a boy sovereign with no real power drowned because of his bloodline. His tragic life is accentuated by the loss of nearly all close relatives. His father, Emperor Takakura (r.1168–1180) died in 1181 at the age of 19. His grandfather and primary supporter Taira no Kiyomori also died in 1181. His other grandfather, Go-Shirakawa was on the other side in the conflict. Indeed, Go-Shirakawa was one of the most powerful people in Kyoto at the time. Emperor Antoku’s grandmother, of course, died with him. If one looks at a list of members of the Taira Clan, one will notice a great many died in 1185. This is touched upon above: the losing Taira leaders committed mass suicide to avoid being killed by the Minamoto forces. There is one notable exception: Taira no Tokuko. Daughter of Taira no Kiyomori and mother of Emperor Antoku, Taira no Tokuko survived the Battle of Dan-no-ura. Though she tried to kill herself by jumping in the sea, she was apparently pulled out by her hair with a rake.
In 1185, she became a nun and lived the rest of her life as such. Below is a poem she wrote during this past period of her life:
“Did I ever dream
That I would behold the moon
Here on the mountain
The moon that I used to view
In the sky o’er the palace.”
Taira no Tokuko died in 1213. Retired Emperor Go-Shirakawa maintained a dominant presence at court until his own death in 1192 at the age of 66. He had maintained power as a cloistered ruler from the time of his abdication in 1158 until his death. At the end of his life, he supported Minamoto no Yoritomo who would go on to establish the first shogunate in Japanese history. The victor of Dan-no-ura, Minamoto no Yoshitsune, ended up committing seppuku after being defeated by forces loyal to his jealous half-brother Yoritomo. Yoshitsune lives on in popular culture with his loyal sidekick Benkei. Emperor Go-Toba remained on the throne until the shogun forced him to abdicate in 1198. From 1198 to 1221, Go-Toba held power at court as a cloistered ruler.
 According to the Tale of the Heike.
 The historical accuracy of the Tale of the Heike, written down 200 years after the events it describes took place, is frequently called into question by historians. In addition, the Imperial Regia of Japan is inaccessible. Even emperors generally do not see these items that are symbolically transferred to them. The jewel is kept at the Imperial Palace in Tokyo, the sword at Atsuta Shrine (Nagoya) and the mirror at the Ise Grand Shrine.
 Tale of Heike. p.772.