Born in 1153, the seventh son of Minamoto no Yoshitomo and a half-brother of Yoritomo. As a child called Imawaka, he was placed at Daigo-ji and raised as a monk, receiving the name Zensho. In 1180, hearing of Yoritomo's uprising, he renounced his vows and joined Kamakura. By marrying Awa no Tsubone (Masako's younger sister), he secured kinship ties with the Hojo and carved out his own position in the shogunate. After Yoritomo's death, power struggles over the succession intensified, and Zensho was reportedly critical of the second shogun Yoriie's administration. In 1203 he was accused of performing curses against the ailing Yoriie and exiled to Hitachi Province (present-day Ibaraki). He was killed shortly after by Yoriie's order. This occurred just before the Hiki Rebellion—when the Hojo moved to depose Yoriie—and his elimination is seen as part of the Hojo's consolidation of power. He reportedly died at around 51. His wife Awa no Tsubone remained at the shogunate and continued to wield influence as a confidante of Masako.

Though trained as a monk, he harbored political ambitions. He tried to secure his position through marriage ties to the Hojo but was consumed by power struggles.

Symbolizes the bloody power structure of Kamakura where Yoritomo's kin were systematically purged. His wife Awa no Tsubone continued to wield influence as Masako's sister.