Lifespan: Kanshō 2 (1461) to 10/15 of Eishō 8 (1511)
Title: Vice Minister of Civil Affairs
Father: Iwamatsu Akizumi
Adoptive Father: Iwamatsu Iezumi (grandfather)
Mother: Daughter of Ninagawa Chikamasa
Siblings: Hisazumi, Akizumi
Iwamatsu Hisazumi served as a daimyō during the late Muromachi period. He was the lord of Nitta-Kanayama Castle in Kōzuke Province.
In 1461, Hisazumi was born as the son of Iwamatsu Akizumi.
Based on the timing of his coming-of-age ceremony, it is surmised that he received one of the characters in his name from Ashikaga Yoshihisa, the ninth shōgun of the Muromachi bakufu. His grandfather, Iwamatsu Iezumi, had connections to the bakufu while his father, Akizumi, also served the bakufu. Moreover, Akizumi’s wife originated from the Ninagawa clan (Ninagawa Chikamasa) which, for generations served as the deputy heads of the mandokoro, a central administrative organ of the bakufu.
After his father, Akizumi, quarreled with his grandfather, Iezumi, in regard to policies toward the Koga kubō, Akizumi was removed from the line of succession so Hisazumi became the designated heir of Iezumi. In 1494, after the death of Iezumi, Hisazumi inherited the headship of the clan.
Hisazumi, however, could not prevent the rise to power of the Yokose clan who were retainers of the Iwamatsu, which evolved into a power-struggle. In 1495, Hisazumi clashed with Yokose Narishige and Yokose Kageshige (father and son), and, despite additional forces furnished by Nagao Fusakiyo, Hisazumi was at a disadvantage. Through the intervention of Ashikaga Shigeuji, the Koga kubō, Hisazumi transferred the headship of the clan to his son, Iwamatsu Masazumi, and was forced into retirement. Thereafter, Hisazumi devoted himself to renga, or linked-verse poetry. In the eighth month of 1509, he held a renga event with an instructor named Sōchō who was staying at the Nitta manor, selecting verses from a compilation of poetry primarily from an instructor named Sōgi.
In 1511, Hisazumi died at the age of fifty-one.
At the Shōren Temple in the city of Ōta in Gunma Prefecture, there is a self-portrait of Hisazumi along with renga verses dated in 1501. Together with a replica of a self-portrait of Sesshū, a water and ink artist from the Muromachi period, this precious work is known as the earliest self-portrait in Japan. While lamenting the lowly manner of bushi from the eastern provinces with respect to renga, it states the etiquette for the conduct of renga events.