Emperor Antoku in the context of "Genpei War"

The Taira (平; Japanese pronunciation: [taꜜi.ɾa]) was one of the four most important clans that dominated Japanese politics during the Heian period of Japanese history – the others being the Minamoto, the Fujiwara, and the Tachibana. The clan is divided into four major groups, named after the emperors they descended from: Kanmu Heishi, Ninmyō Heishi, Montoku Heishi, and Kōkō Heishi, the most influential of which was the Kanmu Heishi line.

In the twilight of the Heian period, the Taira controlled the boy emperor Antoku (himself the grandson of the powerful Kugyō Taira no Kiyomori) and had effectively dominated the Imperial capital of Heian. However, they were opposed by their rivals the Minamoto clan (the Genji), which culminated in the Genpei War (1180–1185 AD). The five-year-long war concluded with a decisive Taira defeat in the naval Battle of Dan-no-Ura, which resulted in the deaths of Antoku and Taira leaders. Following the war, the victorious Minamoto established Japan's first shogunate in Kamakura. The name "Genpei" comes from alternate readings of the kanji "Minamoto" (源 Gen) and "Taira" (平 Hei).

The Battle of Dan-no-ura (壇ノ浦の戦い, Dan-no-ura no tatakai) was a major sea battle of the Genpei War, occurring at Dan-no-ura, in the Shimonoseki Strait off the southern tip of Honshū. On April 25, 1185 (or March 24, 1185 by the official page of Shimonoseki City), the fleet of the Minamoto clan (Genji), led by general Minamoto no Yoshitsune, defeated the fleet of the Taira clan (Heike). The morning rip tide was an advantage for the Taira, but turned to their disadvantage in the afternoon. The young Emperor Antoku was one of those who died among the Taira nobles.

Taira no Tokiko (平 時子; 1126–1185) was a Japanese aristocrat from the Heian period. She was the concubine of Taira no Kiyomori, mother of Taira no Tokuko, and grandmother of Emperor Antoku. Later she took the vows to become a nun, after which she was generally referred to by her Buddhist name as the "Nun of the Second Rank" (二位尼, Nii no Ama).

After Kiyomori's death in 1181, Tokiko's son, Taira no Munemori, became the head of the Taira clan. After this, she became the representative pillar of the Taira clan. According to The Tale of the Heike, Taira no Tokiko drowned herself during the Battle of Dan-no-ura together with her grandson, Taira no Tokushi.