Her contributions were considered so significant that she was posthumously inducted to the Senior First Rank of the Imperial Court, the highest honor that could be conferred by the Emperor of Japan.

During their relationship, Lady Saigō influenced Ieyasu's philosophies, choice of allies, and policies as he rose to power during the late Sengoku period, and she thus had an indirect effect on the organization and composition of the Tokugawa shogunate.

[1] Once she was in a respected and secure position as the official concubine and mother to Ieyasu's heir, Lady Saigō used her influence and wealth for charitable purposes.

The bestowal of a title depended on social class and the relationship with her samurai lord, such as whether she was a legitimate wife or a concubine, and whether or not she had had children by him.

[7][8] The Saigō family was one branch of the distinguished Kikuchi clan of Kyushu that had migrated northward to Mikawa Province in the fifteenth century.

In 1524, the forces of Matsudaira Kiyoyasu (1511–1536), the grandfather of Tokugawa Ieyasu, stormed and took the Saigō clan's headquarters at Yamanaka Castle during his conquest of the Mikawa region.

[12] Following the Battle of Okehazama (1560), Saigō Masakatsu attempted to re-assert the independence of the clan while yielding some land concessions to the Imagawa.

[16] Lady Saigō's father was Tozuka Tadaharu [ja] of Tōtōmi Province, under direct control of the Imagawa clan.

[10] This view contradicts a common impression which maintains that Ieyasu was a ruthless leader who treated all the women in his life, and all of his offspring, as commodities to be used as needed to serve the clan or his own ambitions.

[30][31] Starting around the time of the Battle of Mikatagahara (1573), perhaps in its aftermath, Ieyasu began to confide in Oai and sought her counsel on various matters.

[7] While her manners and gentility were exemplary, she could, when the occasion warranted, be outspoken or sarcastic in speech, the probable result of growing up around rustic warriors in a remote castle outpost.

[11][26] Bearing the child of a powerful samurai, especially a son, was one way an ambitious young woman of the period could elevate her status, ensure a comfortable life, and guarantee the prosperity of her family.

[10] Unlike these courtesans, Oai already had the attention of Ieyasu, which would have undermined the ambitions of some and very likely made her a target of resentment, hostility, and the intrigues that were common in Japanese harems.

[10][33][34] While Ieyasu's marriage was arranged for political reasons, and many of his later concubines were chosen in the same spirit, it is thought that he chose his relationship with Lady Saigō.

[7][8][10] Moreover, Ieyasu valued her for her intelligence and sound advice and it is believed that he enjoyed her company and calm demeanor as well as their common background in Mikawa province.

[28] Because she suffered a high degree of myopia, she often donated money, clothing, food, and other necessities to blind women and organizations that assisted them.

[40] She eventually founded a co-operative school with living quarters near Ryūsen-ji that assisted indigent blind women by teaching them how to play the shamisen (traditional stringed instrument) as a vocation, and helped them to find employment.

They played pieces from a sanctioned repertoire, and operated under a strict code of rules on behavior and permissible business transactions intended to maintain an upstanding reputation.

After their victory at the siege of Odawara Castle in 1590, Ieyasu agreed to relinquish all of his domains to Hideyoshi in exchange for the Kantō region to the east.

[48][49] The following year, he had Ryūsen-ji moved from Yunoki to KōyamachiNote d near Sunpu Castle and attended Buddhist funeral rites conducted in honor of the late Lady Saigō on the anniversary of her death.

[7] In 1628, Tokugawa Hidetada, by then the retired second shōgun, attended ceremonies conducted in honor of his late mother on the anniversary of her death.

[7][40] Her status was later upgraded to Senior First Rank, the highest and most prominent award, then or now, bestowed by the Emperor to a few subjects outside the Imperial family who had significantly and positively affected the history of Japan.

[51] In 1938, the mausoleum of Lady Saigō at Hōdai-in, which consisted of a five-tiered stupa over her grave and a sanctuary for the veneration of her spirit, was designated an Important Cultural Property.

[55][56] The daughter of Masako, and thus great-granddaughter of Lady Saigō, was Princess Okiko (1624–1696),[57] who acceded to the Chrysanthemum Throne in 1629 as Empress Meishō.