The affair of the last T'ang emperor in China and his beautiful concubine, Yang Kwei-fei was the great love story of the age and often mentioned in ancient Chinese and Japanese literature.

"The Song of Unending Sorrow," by Po Chu-i (772-846), was the most popular Chinese poem in Heian Japan. With some embellishment, it recounted the true story of how Yang Kwei-fei (Yokihi in Japanese) rose from obscurity to win the heart of an emperor, before causing his downfall and that of the entire T'ang Dynasty.

Emperor Hsuan Tsung, a grandson of Empress Wu Zetian (Wu-chao, Wu-hou) who ruled from 713-756, was a wise and forward-looking ruler during the early years of his reign. Yang Kwei-fei was originally married to one of his sons in 736, at the age of 18. The emperor, already in his 50s, quickly became infatuated with her and, in 741, she abandoned her husband and entered a Taoist nunnery. By 745, the emperor had arranged for his son to marry another woman and made Yang Kwei-fei (Yang Guifei, Yang Kuei-fei, Yang Gueifei) his "Precious Consort."

From this time on, Hsuan Tsung neglected affairs of state and allowed his court to lapse into decadence. Meanwhile, Yang Kwei-fei caused something of a scandal with her close relationship with An Lu-Shan, a powerful general of Turkic origin. Eventually she adopted the corpulent, 48-year-old general.

A variety of natural disasters and two military defeats caused unrest in the empire, culminating in a rebellion led by An Lu-shan in 755. As the victorious rebel forces advanced on the capital, Hsuan Tsung and his court fled towards Szechwan. On the way, the imperial guard mutinied and killed Yang Kwei-fei's brother, the prime minister. Blaming the Yang family for the empire's troubles, the troops forced the emperor to have his beloved concubine strangled.

An Lu-shan's power didn't last long, however. He was assassinated by his son and eventually the T'ang dynasty regained control. When Hsuan Tsung finally returned to the capital, he was seized by remorse and tried using a Taoist priest to contact Yang Kwei-fei in the netherworld.

According to the poem, the priest manages to contact her, bringing back half a gold hair comb, which the emperor knew belonged to her, and a message:

And she sent him, by his messenger, a sentence reminding him of
vows which had been known only to their two hearts:
'On the seventh day of the seventh month, in the Palace of Long Life,
We told each other secretly in the quiet midnight world
That we wished to fly in heaven, two birds with the wings of one,
And to grow together on the earth, two branches of one tree.'
... Earth endures, heaven endures; sometime both shall end,
While this unending sorrow goes on and on forever.

This yearning to find a lost loved one is a theme that occurs twice in The Tale of Genji. Both Genji and his father lose someone dear to them.

The "seventh day of the seventh month" refers to the legend of the herdboy and the weaver girl, represented by the stars Altair and Vega. The two lovers are separated by the Milky Way, and only meet once a year on the seventh day of the seventh lunar month, crossing the heavens on a bridge of magpies. This legend is still celebrated in Japan by the Tanabata Festival.

The events at court leading up to the An Lu-shan rebellion are described in A Floating Life: The Adventures of Li Po - a fictionalized biography of the extraordinary poet who was a witness to the events. A rather different version of the story is shown in Kenji Mizoguchi's movie, Princess Yang Kwei-fei (also on VHS). In Mizoguchi's version, Yang Kwei-fei is a woman manipulated by family and politicians, an innocent victim of fate.

It is said that when Yang Kwei-fei died, the emperor missed her so much that he had her sculpture made in the image of Avalokitesvara (Kannon), which was brought to Sennyu-ji Temple in Kyoto by the priest Tankai in 1255. It is located in a small Kannon-do in the temple grounds and known as the Yokihi Kannon or Empress Yang-Avalokitesvara.

The Kannon-do at Sennyuji is one of the 33 places of worship on the Rakuyo ("Loyang") Pilgrimage.