Satō Tadayoshi served as a bushō during the Sengoku and Azuchi-Momoyama periods.  He also had the names of Kii-no-kami and Sanshō.  Tadayoshi served as the lord of Kajita Castle in Mino Province.  He belonged to the kunishū, or provincial landowners, serving the Saitō clan of Mino.

Tadayoshi was born as the son of Satō Kiyofusa and his mother was Tokurin-Myōfuku.

Initially, he was known as Kuwabara Ukonemon-no-jō but, by 1565, he is surmised to have adopted the surname of Satō.  Under other theories, Ukonemon-no-jō referred to his son, Tadayasu, or alternatively, was an unrelated individual.

Tadayoshi was a kokujin, or provincial landowner, in Mino, descending from the lineage of Fujiwara no Hidesato, a noble from the Heian period.  Tadayoshi supported Saitō Dōsan when Dōsan usurped Toki Yoriaki. Later, in 1556, Tadayoshi backed Dōsan’s son, Saitō Yoshitatsu, in the rebellion against Dōsan at the Battle of Nagarawagawa.

Tadayoshi received a written commendation for his contributions in the battle, in addition to landholdings including Nishitawara (400 kan), Kamino (300 kan), and the Kamo and Mugi districts (4,389 kan).

After his death from illness in 1561, Yoshitatsu was succeeded by an illegitimate son, Saitō Tatsuoki.  In the era of Tatsuoki, Tadayoshi entered into a three-way alliance with Nagai Michitoshi (the lord of Seki Castle) and Kishi Nobuchika (the lord of Dōhora Castle) to defend against attacks by Oda Nobunaga of neighboring Owari Province.  However, Tadayoshi and his son, Tadayasu, dispatched a messenger named Umemura Ryōtaku to collude with Nobunaga.  Tadayoshi secured permission from Nobunaga to receive the land taxes from the Kamo, Mugi, and Gujō districts and, after garnering control of these areas which in turn were recognized as his fief.

Later, a rumor circulated that the Western Mino Group of Three (Andō Morinari, Inaba Yoshimichi, and Ujiie Naomoto) had switched their allegiance from the Saitō to the Oda.  This caused the Kishi to suspect that Tadayoshi may also collude.  To mitigate this risk, Kishi Nobuchika arranged to adopt Tadayoshi’s daughter, Yaeryoku, to wed one of his sons, whereupon Yaeryoku served as both a hostage and daughter-in-law of Nobuchika.

In the eighth month of 1565, after Nobunaga invaded Mino, Tadayoshi obeyed his secret promise to support the Oda.  Upon learning of the betrayal, Kishi Nobukata skewered Tadayoshi’s daughter, Yaeryoku, with a bamboo spear and exposed her on a cross on Mount Nagaomaru facing Kajita Castle.  That night, a veteran of the Kajita army named Nishimura Jirōbei recovered Yaeryoku’s body under cover of darkness and buried her remains at the Ryūfuku Temple.

After Nagai Michitoshi joined Hida Tadamasa in a bid to capture Kajita Castle (which had switched allegiance to the Oda), Tadayoshi deployed with Kishi Nobuchika of nearby Dōhora Castle.  Tadayoshi served in the rear guard from Seki Castle.  On 8/28, the Oda army commenced attacks against Dōhora Castle.  Having colluded with the Oda, Tadayoshi and his son, Tadayasu, supported the Oda in the attack on Dōhora.  After a six-hour battle, Dōhora fell in an event known as the Siege of Dōhora Castle.  That day, Nobunaga lodged at the residence of Tadayasu, and Tadayoshi and his son were moved with tears of gratitude.

After the fall of Dōhora Castle, attacks were launched against Kajita Castle by Nagai Michitoshi from the east and Hida Tadamasa from the west in an event known as the Battle of Seki and Kajita.  Violent clashes occurred at the Kajita-Nunomaru moat, but, with reinforcements led by Saitō Toshiharu on the side of the Oda, the members of the castle garrison fought valiantly, repelling the assault by the Nagai forces.  To the northeast, Tadayoshi engaged in battle against forces led by Hide Tadamasa at the Kawaura River which served as a natural barrier.  Tadayoshi himself took part in five clashes, repelling Tadamasa.  In the course of this conflict, his son, Tadayasu, was killed in action.

In 1567, upon orders of Nobunaga, Tadayoshi adopted Saitō Toshiharu and assigned him to Kajita Castle.  Tadayoshi retired to the neighboring village of Ibuka and constructed the Ryūfuku Temple in Kajita as the family temple of the Satō family.  Six documents signed by Tadayoshi and displaying his seal are kept at this temple.

With respect to the succession to the family from Tadayoshi to Toshiharu, from 1565 to 1567, a struggle arose between Tadayoshi’s son (Tadayasu) and his younger brother (Masanobu), during which Masanobu killed Tadayasu and forcible took Kajita Castle.  However, this occurred shortly before the attack on Inabayama Castle so, having drawn the ire of Nobunaga, Tadayoshi retired while Masanobu was either transferred to Muge Hachiman.  There is also a theory that his descendants suppressed the dishonorable incident by stating that Tadayasu was killed in battle.

In the seventh month of 1567, when Yamashina Tokitsugu, a high-ranking noble from Kyōto, came to stay in Gifu, Tadayoshi enjoyed friendship with him.  During this time, Nobunaga told him to display a kettle that was owned by Yoshitatsu, but it went missing, so seventeen kunishū, or provincial forces, including Tadayoshi, were at first ordered to commit seppuku, but the incident was later resolved.

On 5/5 of Tenshō 6 (1578), Tadayoshi died of illness and was interred at the Ryūfuku Temple.

Character

Among the members of the Mino-Saitō clan, Tadayoshi was a powerful member of the provincial forces.  After switching his loyalties to the Oda clan, and after his daughter, Seishitsu-in, wed Saitō Toshiharu, who came to serve as the second-generation lord of Kajita Castle as an adoptee of Tadayoshi.

In a portrait, he is shown with a hood, holding a sutra scroll in his left hand and ceremonial sceptre in his right hand.  He is surmised to have worn formal dress and his hood in times of peace and war.  Tadayoshi was described as courageous, benevolent, and intelligent.  He had a welcoming countenance, displaying a fan in one hand.  Commanding his forces, he deployed his forces in crane-wing and fish-scale formations, winning numerous contests.

After retiring, Tadayoshi spent time with nobles in Kyōto, providing a glimpse of his sociable character.  On the one-year anniversary of his death, his son-in-law, Toshiharu, lit incense and recited Buddhist verses, later adopting the name of Tadatsugu in honor of his adoptive father.