Masako, one of the most formidable political figures to take a place on the stage of Japan's warrior government, was the daughter of Hôjô Tokimasa and was married to Minamoto Yoritomo. Following the death of her husband (who had become the first Minamoto shôgun in 1192), Masako took up a nun's habit, accepting the tonsure from the priest Gyôyû in 1199. She by no means retired from politics, however, and worked closely with her father to secure the power of the Hôjô in Kamakura. One of her first actions was to form a council of 'elders' (the shukuro) to moderate the power of her own son, the headstrong 2nd shôgun Yoriie. Yoriie was infuriated by the measure, and turned for support among the Hiki clan, the Hôjô's chief political obstacle at the time. The Azuma Kagami relates that Masako overheard Yoriie plotting with the Hiki to kill Hôjô Tokimasa, and that Masako dutifully reported this to her father. Regardless of the truth to this story - or in what way it played out - the result was that Tokimasa moved first, eliminating the Hiki leadership in the fall of 1203. Deprived of his allies, Yoriie was forced into exile in Izu Province and was later murdered. In his place, the eleven-year old Sanetomo was installed, and here we may see the signs of developing cracks between Tokimasa and Masako, for the former had Sanetomo removed from Masako's residence and taken to his own. At this point, Tokimasa became the most powerful man in Kamakura and created the mandokoro office through which he might exercise his authority as regent to Sanetomo. Yet his pinnacle of success was to be short-lived. In 1205, Masako and her brother Yoshitoki ousted Tokimasa, ostensibly due to a supposed plot on his part to kill Sanetomo. Yoshitoki, still smarting from what he felt was an unjustified sentence passed on the Hatakeyama clan (they were eliminated on the suspicion of treasonous designs), publicly declared his support for Sanetomo, and according to the Azumi Kagami Tokimasa felt it wise to step down and retire.
Masako proved as useful to her brother as she had once been to their father, and in 1218 she was dispatched to Kyoto to suggest that one of Retired Emperor Go-Toba's sons be adopted as heir to the childless Sanetomo. Sanetomo was in fact assassinated the following year, and Go-Toba refused to offer a successor and in any case attempted a return to Imperial authority in 1221 that ended in failure.
Yoshitoki died in July 1224 and his passing inspired a conspiracy by the Iga family, who hoped to use the powerful Miura Yoshimura to topple the Hôjô and replace them in Kamakura. Masako learned of the threat and personally rushed to see Yoshimura, extracting a promise that he would stand by the Hôjô, effectively derailing the conspiracy before it had begun. Her brother Yasutoki safely assumed the regency, and the following year she died at the age of 69.
Masako was a remarkable figure and such was her political ability and sway in Kamakura that she was given the nickname of 'ama-shôgun', or the nun-shôgun. The Kamakura nendaiki in fact indicates her name in its list of shoguns, ruling from 1219 until her death in 1225, during what would otherwise be rendered a multi-year period with no shogun at all, until Kujô Yoritsune came to Kamakura from Kyoto in 1226 to assume the title.
- Initial text from Samurai-Archives.com FWSeal & CEWest, 2005