Cloistered Emperor
In 1179, Minamoto no Yoritomo, the Minamoto exile from Kyoto, fell in love with Tokimasa's daughter, Masako. In around 1180, they wed. That same year, Prince Mochihito, a son of Cloistered Emperor Go-Shirakawa and a brother of Cloistered Emperor Takakura and thus an uncle of Emperor Antoku, who was half-Taira and had been placed on the throne by the Taira, believed the Taira had denied him the throne and called on the exiled Minamoto leaders to go to war and oust the Taira. Yoritomo declared war on the Taira, thus gaining his father-in-law, Tokimasa's support and the support of the Hōjō clan. That same year, Masako and Yoritomo had a daughter, Ō-hime, Tokimasa's first grandchild.