Emperor Kōnin
Niigasa was a daughter of Yamato no Ototsugu (和乙継). She became a concubine of Prince Shirakabe (白壁王), grandson of Emperor Tenji, and bore Prince Yamabe ("山部王") in 737 and Prince Sawara ("早良王") in 750. Prince Shirakabe was married to Princess Inoe ("井上内親王"), a daughter of Emperor Shōmu (聖武天皇) in 744. When Empress Kōken died in 770, Shirakabe was appointed her successor and acceded to the throne as Emperor Kōnin. Princess Inoe and her son, Prince Osabe, were nominated as the Empress and the crown prince respectively, because of her noble birth.