was a retainer

Retainer

Retainer may refer to:* Retainer , a person, especially a soldier, in the service of a lord in the late Middle Ages** Retainer sacrifice, the sacrifice of a human servant* Retainer...

 under the Toyotomi clan

Toyotomi clan

Originating in Owari Province, the served as retainers to the Oda clan throughout 16th-century Japan's Sengoku period. -Unity and Conflict:The most influential figure within the Toyotomi was Toyotomi Hideyoshi, one of the three "unifiers of Japan." Oda Nobunaga was another primary unifier and the...

 during the late Sengoku period

Sengoku period

The or Warring States period in Japanese history was a time of social upheaval, political intrigue, and nearly constant military conflict that lasted roughly from the middle of the 15th century to the beginning of the 17th century. The name "Sengoku" was adopted by Japanese historians in reference...

 of feudal Japan. Residing within Mino Province

Mino Province

, one of the old provinces of Japan, encompassed part of modern-day Gifu Prefecture. It was sometimes called . Mino Province bordered Echizen, Hida, Ise, Mikawa, Ōmi, Owari, and Shinano Provinces....

 during his early life, Mitsuyasu took up arms in support of the Saitō clan

Saito clan

The was a Japanese clan in Mino Province during the Sengoku period in the 16th century. According to records, the Saitō clan descended from the Fujiwara clan...

 and its leader, Saitō Dosan

Saito Dosan

was a daimyo who dramatically rose and also fell from power in Sengoku period Japan. He was also known as the for his ruthless tactics.-Life:Originally a wealthy merchant from Yamashiro Province , he entered the service of Nagai Nagahiro of Mino Province , assuming the name Nishimura Kankurô.He...

.

When Saitō Tatsuoki

Saito Tatsuoki

was a daimyo in Mino Province during the Sengoku period and the third generation lord of the Saitō clan. He was a son of Saitō Yoshitatsu, and a grandson of Saitō Dōsan. He was also a nephew of Oda Nobunaga's first wife, Nōhime, herself a daughter of Saitō Dōsan....

 succeeded to the clan leadership, Mitsuyasu defected to Oda Nobunaga

Oda Nobunaga

was the initiator of the unification of Japan under the shogunate in the late 16th century, which ruled Japan until the Meiji Restoration in 1868. He was also a major daimyo during the Sengoku period of Japanese history. His opus was continued, completed and finalized by his successors Toyotomi...

 in 1567, expanding under the latter's rulership for many years following. Rising to become a general while under the service of Toyotomi Hideyoshi

Toyotomi Hideyoshi

was a daimyo warrior, general and politician of the Sengoku period. He unified the political factions of Japan. He succeeded his former liege lord, Oda Nobunaga, and brought an end to the Sengoku period. The period of his rule is often called the Momoyama period, named after Hideyoshi's castle...

 by the 1580s, Mitsuyasu was rewarded with property valued at 240,000 koku

Koku

The is a Japanese unit of volume, equal to ten cubic shaku. In this definition, 3.5937 koku equal one cubic metre, i.e. 1 koku is approximately 278.3 litres. The koku was originally defined as a quantity of rice, historically defined as enough rice to feed one person for one year...

within Ōmi Province

Omi Province

is an old province of Japan, which today comprises Shiga Prefecture. It was one of the provinces that made up the Tōsandō circuit. It is nicknamed as .Lake Biwa, Japan's largest lake, is located at the center of the province...

, encouraging him to serve under his lord throughout the first Korean campaign in 1592 and 1593.

Following his participation in the Korean campaign, Mitsuyasu died of a sudden illness while returning home. At the time of his death, he was beginning construction on Kurono Castle

Kurono Castle

was a castle built in Mino Province in Japan in 1597. Though the castle spanned the Sengoku and Edo periods, it barely did so as the castle was demolished in 1610. The castle supported the Saitō, Oda and Toyotomi clans.-History:...

 in Mino Province, but his death passed control of the castle to his son, Katō Sadayasu, who completed the construction.