Irobe Mitsunaga served as a bushō during the Azuchi-Momoyama and early Edo periods.  He was a senior retainer of the Uesugi clan and, in the Edo period, of the Yonezawa domain.  Mitsunaga served as the lord of Hirabayashi Castle in Echigo Province, and then as the lord of Kaneyama Castle in Dewa Province.

In 1587, Mitsunaga was born as the son and designated heir of Irobe Nagazane, a senior retainer of the Uesugi clan and the lord of Hirabayashi Castle in the village of Hirabayashi in the Koizumi manor of the Iwafune District of Echigo.  In 1592, upon the death from illness of his father, Mitsunaga, while in his youth, inherited the headship of the Irobe clan.  According to the will of his father, Mitsunaga wed as his formal wife the younger sister of Naoe Kanetsugu (under alternate theories, she was his second daughter).  Thereafter, Kanetsugu served as a guardian of Mitsunaga to support him in ruling the family until Mitsunaga’s coming-of-age ceremony.

In 1598, in connection with the transfer of the Uesugi clan to Aizu in Mutsu Province, Mitsunaga became the lord of Kaneyama Castle in the Okitama District of Dewa.  In 1600, for the Battle of Keichō Dewa, he was assigned responsibility for the vanguard forces.  After the Uesugi clan was subject to a reduction of their fief, Mitsunaga governed the village of Kubota in the Okitama District.  In 1602, he attended his coming-of-age ceremony and received the character of “tsuna” from Kanetsugu and adopted the name of Tsunanaga.  In 1614, Mitsunaga participated in the Winter Campaign of the Siege of Ōsaka.  On 1/15 of Kanei 1 (1624), he was conferred the title of Governor of Nagato, and, in the eleventh month of 1626, appointed as the Head of the Board of Retainers.

On 6/2 of Kanei 17 (1640), Mitsunaga died at the age of fifty-four.  He was succeeded by his adopted son, Irobe Toshinaga. 

Kanetsugu was relied upon by the Irobe clan to back-up Mitsunaga and, after the death of Kanetsugu in 1620, until the end of the Edo period, the Irobe clan served as senior retainers of the Yonezawa domain. 

Descendants

Descendants included, among others, Irobe Yasunaga (Matashirō) who was a chief retainer in Edo at the time of the Akō Incident.  On 3/14 of Genroku 14 (1701), Asano Naganori, the third lord of the Harima-Akō domain, was forced to commit seppuku in the Matsuno corridor at Edo Castle after attacking a noble named Kira Kōzuke-no-suke Yoshihisa on an important ceremonial day for the Edo bakufu.  This prompted the chief retainer of the Harima-Akō domain named Ōishi Kura-no-suke Yoshio to later lead a band of forty-seven bushi to attack the Kira residence and slay Yoshihisa.  This well-known event gave rise to a dramatization called chūshingura. 

Other descendants included Irobe Terunaga (Yasaburō), a senior retainer of the Yonezawa domain who, in 1773, was punished in connection with the Seven Families Disturbance at the time of political reforms to the Yonezawa domain by Uesugi Yōzan.  Finally, Irobe Hisanaga was killed in action in Niigata while serving as governor-general of the Yonezawa domain during the Boshin War in 1868.  Over the generations, adopted children succeeded to the headship of the clan so this was not a direct bloodline from the era of Mitsunaga.

Character and Anecdotes

When Mitsunaga was serving as the lord of Kaneyama Castle, he had servants serve a meal while hosting a visit from Naoe Kanetsugu.  When Kanetsugu noticed that the broth soup included wild goose meat, he said to Mitsunaga that adding the goose meat was a luxury and did not partake in the soup.  Later, the servant was dismissed by Kanetsugu.

On 10/18 of Keichō 9 (1604), Mitsunaga received a training manual for a sport of kickball called kemari and a 免翰 from a noble named Asukai Masatsune.