Kiso Yoshimasa served as a bushō and daimyō during the Sengoku and Azuchi-Momoyama periods.  He served as the nineteenth head of the Kiso clan who were landlords of Kisodani in Shinano Province.

The Kiso regarded themselves as well-established lineal descendants of Minamoto no Yoshinaka, a high-ranking bushō from the closing years of the Heian period.  That view, however, was based on a genealogy created during the Nanbokuchō period.  Their direct descendants purported to be from the Fujiwara no Hidesato line of the Fujiwara-Hokke.

Origins

In 1540, Yoshimasa was born as the lineal heir of Kiso Yoshiyasu.  Initially, he joined with the Ogasawara and Murakami clans to resist a campaign led by Takeda Harunobu (Shingen) known as the Invasion of Shinano.  In 1555, after further attacks, he surrendered to the Takeda family.  The Kiso controlled the border area with Mino and Hida provinces so Shingen had his third daughter, Marihime (later known as Shinryūin), wed Yoshimasa and, as relatives of the Takeda family, provided official recognition of the rights of the Kiso clan to Kisodani.  There are no references in authenticated sources from this period in regard to a bridal procession for Marihime.  Primary retainers of the Kiso and relatives were in Kōfu as hostages while the administration by the Kiso of their territory was closely supervised by the Takeda family.  Yoshimasa was therefore compelled to accept Shinano as a vassal state of Kai Province.  As a result, Kisodani became the front line of the Takeda family for invasions into Mino and Hida.  In 1560, he made a religious pilgrimage climbing Mount Ontake in Shinano.

In the eighth month of 1573, Yoshimasa stormed the Kawaori prison in the Ena District of Mino Province.  Next, he assaulted Naegi Castle held by the Naegi-Tōyama clan.  In 1574, upon orders of Takeda Shingen, he attacked Adera Castle in the Ena District, killing its lord, Tōyama Tomoshige of the Atera-Tōyama clan.  Following the death from illness of Shingen in 1573, and a defeat at the First Siege of Takatenjin Castle in the fifth and sixth months of 1574, the Takeda family began to show signs of decline, raising concerns as to its future.  Meanwhile, Yoshimasa resented the heavy taxes and increased levies for the construction of Shinpu Castle imposed by his brother-in-law, Takeda Katsuyori.  On 8/26 of Tenshō 9 (1581), Yoshimasa received a letter from Tōyama Tomotada of the Naegi-Tōyama clan in regard to preparations by Oda Nobutada for an attack against the Takeda.  In the first month of 1582, Yoshimasa responded via Tomotada to solicitations from the Oda clan to betray the Takeda, whereupon he tendered his younger brother, Agematsu Yoshitoyo, as a hostage and then abandoned Katsuyori.  This provided an opportunity for Nobunaga to launch the Conquest of Kōshū.  Katsuyori responded to these developments by executing several hostages including Yoshimasa’s seventy-year-old mother, his consort, his thirteen-year-old lineal heir (Sentarō), and his seventeen-year-old eldest daughter (Iwahime), at Shinpu Castle.  Katsuyori then dispatched an army under the command of Takeda Nobutoyo in the direction of Kisodani.  By using tactics favorable to the local topography, as well as having received reinforcements from Oda Nobutada, Yoshimasa was able to repel the Takeda forces at the Torii Pass.

After decimation of the Takeda family

In the third month of 1582, the Conquest of Kōshū by the Oda army resulted in the decimation of the Takeda family.  Thereafter, Yoshimasa served Nobunaga.  Nobunaga awarded Yoshimasa with a nashiji long sword and 100 pieces of gold.  Further, he is said to have given secret orders to grant two districts in Shinano to Yoshimasa.  He assigned a chamberlain to Fukashi Castle (later known as Matsumoto Castle) and, in addition to Kiso, oversaw the Matsumoto and Azumi areas.  Just three months later, instability triggered by the coup d’état against Oda Nobunaga extended to Shinano.  Yoshimasa abandoned his landholdings in northern Shinano.  He targeted Mori Nagayoshi who had fled to Mino, but instead was forced into Kiso-Fukushima Castle while his son, Iwamatsumaru (later Kiso Yoshitoshi), was apprehended.

As a result of Iwamatsumaru becoming a hostage, Yoshimasa was compelled to request bushō in the area, such as Tōyama Tomotada, who opposed Nagayoshi to refrain from attacking the Mori army and instead he acted to facilitate the withdrawal of Nagayoshi.  With the support of Uesugi Kagekatsu of Echigo, former retainers of the Ogasawara clan (the prior landlords of Fukashi) viewed the chaos in the wake of Nobunaga’s untimely death as an opportunity to back Dōsetsusai, the younger brother of Ogasawara Nagatoki (the former military governor of Shinano).  These former retainers captured Fukashi Castle while the Kiso withdrew to their homeland of Kisodani.  Meanwhile, the former territory of the Takeda in Kai led to the Tenshō Jingo Conflict among Uesugi Kagekatsu, Tokugawa Ieyasu, and Hōjō Ujinao.  In the beginning, Yoshimasa followed Ujinao, but, after a defeat in the eighth month of the Gohōjō army at the Battle of Kōshū-Kurokoma, Yoshimasa obeyed the will of Oda Nobutaka (his former lord) and, in the ninth month, switched allegiance to Ieyasu.  He was then promised that, after gathering hostages from other kunishū, or provincial landowners, in Shinano and tendering them to Ieyasu, he would receive official recognition of his rights to the districts of Azumi and Chikuma in addition to Kisodani.  Ieyasu, however, permitted Ogasawara Sadayoshi (the son of Ogasawara Nagatoki) to return as the lord of Fukashi Castle.

After the Battle of Komaki-Nagakute between Ieyasu and Hashiba Hideyoshi in 1584, Yoshimasa abandoned Ieyasu, tendering his third son, Kiso Yoshiharu, and submitting to Hideyoshi.  In the ninth month, he placed Yamamura Yoshikatsu in Tsumago Castle.  Ieyasu sent retainers including Suganuma Sadatoshi, Hoshina Masanao, and Suwa Yoritada to assault the castle, but Yoshikatsu repelled them.  In 1586, after Hideyoshi and Ieyasu reconciled, numerous bushō in Shinano including the Kiso clan came under the command of Ieyasu.  The Kiso thereby lost their independence as a local force.  During Hideyoshi’s subsequent attack against the Hōjō, Yoshimasa could not deploy owing to illness.

Later years

In 1590, accompanying the transfer of Ieyasu to the Kantō, Yoshimasa was awarded by Ieyasu landholdings of 10,000 koku in Ashido in Shimōsa Province and he departed from Kisodani.  Most of the land in Kiso was mountain forest, so there is a theory that Hideyoshi sought these resources and had them seized, granting the land in Ashido in exchange.  In the twelfth month, Yoshimasa arrived in the village of Mikawa in Shimōsa, resided in the Tōen Temple, and developed the Ashido area.  In the third month of 1591, he entered Ashido Castle.  To the south of the castle, a town was planned to open a market.  On 12/12 of Tenshō 18 (1590), Yoshimasa assigned Chimura Yoshishige to serve as a local magistrate in Tōkashi and Hezone for a stipend of 700 koku and in Mihiro for 66 kan.

The date of Yoshimasa’s death is uncertain.  Theories include 2/13 of Bunroku 4 (1595), 3/17 of Bunroku 4 (1595), or 7/13 of Keichō 1 (1596).  He was succeeded by Yoshitoshi.

Yoshimasa’s grave is at the Tōzen Temple (formerly the Tōzen Temple) in Amido in the city of Asahi in Chiba Prefecture.  His ashes were spread in a lake known as the Tsubaki Sea to the west of the castle.  After this became a tideland, his tomb was rebuilt.  In 1671, the Tsubaki Sea was reclaimed and became arable land called Higata-Hachimangoku.  In a corner of this area resides the Kiso Yoshimasa Historical Park and a bronze statue of Yoshimasa.

Descendants

After the death of Yoshimasa, Yoshitoshi engaged in acts of violence including the murder of his uncle, Agematsu Yoshitoyo (Yoshimasa’s younger brother), for which, in 1600, he was purportedly removed from his position.  Yoshitoshi became a rōnin and, later, turned to the Gamō clan for support, accompanying the Gamō upon their transfer to Iyo-Matsuyama.  He is surmised to have resided in this location, but after departing from Ashido, there are no authenticated accounts of his whereabouts.  Regarding the removal from his position, this is variously interpreted as exile to Shimōsa or simply as an ouster.  There is a theory that he died in Iyo-Matsuyama in 1629, but this is not substantiated.  His son, Genba Yoshitoki served Hisamatsu-Matsudaira family.  Later, he became a rōnin, or wandering samurai, while his sons relied upon relatives including the Chimura and Yamamura clans and, with their backing, were engaged in service by the Owari domain.

Yoshimasa’s third son, Yoshiharu (Yoshinari), responded to a solicitation from Toyotomi Hideyori to rōninto join the Siege of Ōsaka, and entered Ōsaka Castle, but was killed in action.  His fourth son, Yoshikazu (Yoshimichi), together with his mother, Marihime (Shinryūin), lived in seclusion in Kisodani, but further details are unknown.

The Kiso were extinguished as a daimyō family, but the vestiges and landholdings of the family (totaling 16,200 koku) were inherited by retainers (relatives) including the Chimura and Yamamura clans.  In the Edo period, Agematsu Yoshitsugu (the son of Yoshimasa’s nephew, Yoshishige) became an attendant of Uesugi Sadakatsu and served the Yonezawa domain.