Saitō Yoshitatsu served as a bushō and sengoku daimyō of Mino Province during the Sengoku period.  Yoshitatsu was the second head of the branch of the Saitō clan founded by his father, Saitō Dōsan.  Under an alternate theory, he was the first head of the Mino-Isshiki clan.  Yoshitatsu was a member of the shōbanshū, a group of individuals comprised of members of the family of the deputy shōgun and influential shugo daimyō who accompanied the shōgun during visits outside of the palace as well as for the hosting of banquets.

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On 7/8 of Daiei 7 (1527), Yoshitatsu was born as an illegitimate son of Saitō Toshimasa (later known as Saitō Dōsan).  His mother was a consort named Miyoshino.

During the period from 2/22 to 3/10 of Tenbun 23 (1554), Dōsan retired so Yoshitatsu inherited the headship of the Saitō clan serving as the deputy military governor of Mino Province and became the lord of Inabayama Castle located on Mount Inokuchi in Mino.  There is a view that Dōsan did not retire on his own accord.  Rather, he lost the trust of his retainers owing to the ineffective governance of his territory so his replacement with Yoshitatsu led to accompanying drama.  According to one account of the history of Mino, Dōsan retired, transferred Inabayama Castle to Yoshitatsu, and moved to Sagiyama Castle.  There are no accounts, however, of his retirement in authenticated records such as the Shinchō-kōki or in other records of Mino, giving rise to a theory that Yoshitatsu succeeded him in 1548 as well as a theory that Dōsan did not in fact retire.

Thereafter, Dōsan concluded Yoshitatsu was a fool, and he turned his attention toward his next younger sons, Saitō Magoshirō and Saitō Kiheiji whom he regarded as clever.  Meanwhile, Yoshitatsu became increasingly dissatisfied with his father’s behavior and policies.  Finally, Dōsan removed Yoshitatsu from the line of succession and attempted to have Magoshirō (who was born to his formal wife, Omi-no-kata) become his designated successor.  He then had the next son, Kiheiji, adopt the name of Isshiki Uhyōe Taifu in association with the prominent Isshiki clan.  As a result, the relationship between Yoshitatsu and Dōsan further deteriorated.

In 1555, Yoshitatsu colluded with his uncle, Nagai Michitoshi, to lure Magoshirō and Kiheiji to Inabayama Castle.  After enjoying drinks, the two brothers were slayed with a sword by a retainer named Hineno Hironari.  In the aftermath of this incident, Dōsan fled to Ōga Castle.

Based on an analysis of one historical account of Mino, there is a theory that Kiheiji survived the assault and was later known as Saitō Toshitaka.  The basis for this connection is that Kiheiji and Toshitaka both used the common name of Genba.  Nevertheless, there is a prevailing counterargument that the theory of his survival is invalid and both brothers were in fact killed.

In the fourth month of 1556, Yoshitatsu confronted Dōsan at the Nagara River.  Yoshitatsu led an army of 17,500 soldiers including former retainers of the Toki clan compared to only 2,700 soldiers on the side of Dōsan.  Yoshitatsu prevailed in this conflict known as the Battle of Nagaragawa.  Around this time, Yoshitatsu employed tactics with rapid movements through the use of detached units to crush members of the Akechi clan and others allied with Dōsan.  Oda Nobunaga came from Owari in an effort to assist Dōsan but did not arrive in time.  After engaging in limited clashes against Yoshitatsu’s forces, the Oda withdrew.  At this time, Yoshitatsu’s youngest brother, Saitō Toshiharu, defected to the Oda family in Owari and, after receiving one of the characters from the name of Nobunaga, changed his name to Nagatatsu.

Amidst ongoing battles against the Oda clan of Owari, Yoshitatsu was permitted by Ashikaga Yoshiteru, the thirteenth shōgun of the Muromachi bakufu, to use the surname of the Isshiki clan whereupon he changed his surname from the Saitō clan serving as the deputy military governors of Mino.  In 1558, he was invested with the title of Vice Minister of Civil Affairs and traveled to Kyōto in 1559 to meet Yoshiteru.  He then formed an alliance with Rokkaku Yoshiharu of southern Ōmi and fought against Azai Hisamasa of northern Ōmi.  Owing to more intense attacks by Oda Nobunaga, Yoshitatsu was beset by unfavorable circumstances and unable to expand his power.

In 1561, Yoshitatsu was appointed as the Master of the Eastern Capital Office, but on 5/11 of the same year, died of illness.  He was either thirty-three or thirty-five years old.  Yoshitatsu was succeeded by his son, Saitō Tatsuoki.

Character and anecdotes

There is a theory that Yoshitatsu’s father was not Dōsan but rather Toki Yoriaki.  Under this theory, Dōsan’s consort, Miyoshino, was already pregnant with Yoshitatsu at the time that she became a consort of Dōsan.  This view, however, lacks authentication and there is a letter from a third party recognizing Dōsan as the father of Yoshitatsu.  This letter, dated in 1560, is from Rokkaku Yoshikata and addressed to a retainer.

Perhaps to avoid the disgrace of having murdered one’s father, Yoshitatsu adopted the name of Isshiki Sakyō Taifu, with the Isshiki being prominent members of the Ashikaga clan.  His lord’s family, the Toki, adopted Shigeyori from the Isshiki clan, and a third-generation grandson, Yorihide, adopted the name of the Isshiki clan.  It is surmised the Isshiki surname was adopted to assert his own legitimacy.  Yoshitatsu’s grandfather on the side of his mother, Miyoshino, was Isshiki Yoshitō, the military governor of the Chita District of Owari.  In addition, Isshiki Yoshikiyo may have been the father of Miyoshino.  There is a theory that former retainers of the Toki clan backing Yoshitatsu including from the Kuwahara, the Andō, the Hineno, and the Takenokoshi clans changed their surnames to Nobenaga, Iga, Ujiie, and Nariyoshi which had ties to retainers of the Isshiki clan, but the change of surnames of members of the band of retainers of the Isshiki who in turn were retainers of the Saitō clan occurred during the governance of Saitō Tatsuoki in 1561 (after the demise of Yoshitatsu).

Taking advantage of the rumor that he was not the natural son of Dōsan provided a means to avoid the dishonor of killing his father and, by adopting the Isshiki surname, Yoshitatsu was able to amass 17,500 kokujin from Mino under his command.  Although the Isshiki and the Toki were both shugo daimyō families, the Isshiki, as members of the Ashikaga clan, were of a higher status than the Toki clan who originated from the Mino-Genji.  There is also a theory that, by obtaining recognition as the head of the Isshiki clan, Yoshitatsu refuted the propriety of the governance of Mino by the Toki clan.  Consequently, this justified the expulsion of Toki Yoriaki.

Dōsan wrote a document similar to a will by which he sought to transfer Mino Province to Nobunaga indicating that Dōsan refused to accept Yoshitatsu to the end.

In 1559, when Oda Nobunaga traveled to Kyōto accompanied by only a small party, Yoshitatsu is said to have dispatched a small force armed with arquebuses in a bid to assassinate him while on the road.

Yoshitatsu was a large individual who stood approximately 197 cm in height.

Yoshitatsu contracted leprosy which caused him to die early.  According to one account, instead of leprosy, Yoshitatsu, along with his wife and son, contracted another rare disease and all died at the same time.

After the elimination of Dōsan, Yoshitatsu adopted the name of Hanka.  This is the name of an individual who, during the era of the Tang dynasty (618 to 907) in China, murdered his father as a result of unavoidable circumstances.  Per the Shinchō-kōki, Yoshitatsu used this name as a reflection of his own situation.  The veracity of the legend associated with Hanka, however, is not confirmed.  Moreover, Yoshitatsu used this name prior to the date when his killed his father.  According to one account, he issued a prohibition to the Mie Temple under the name of Hanka in the twelfth month of 1555.  Therefore, the theory that Yoshitatsu adopted this name to assuage his guilt after the inspection of heads including that of his father appears erroneous.  It has been established that he adopted the name of Hanka after committing to engage in battle against his father.  According to one scholar, the slaying of Dōsan (his adoptive father) enabled Yoshitatsu to avenge the loss of his natural father, Toki Yoriaki, which constituted an act of filial piety.  Under this theory, Yoshitatsu’s frame of mind was that he was in a position where he had to fight against his father so if he considered himself to be like Hanka, then he felt empowered to go on the offensive.

One scholar criticized existing theories regarding the succession from Dōsan to Yoshitatsu as well as Dōsan’s death in battle.  Noting the lack of documents issued by Dōsan in Mino, he concludes that Dōsan was forcibly removed by senior retainers opposed to his neglectful governance of the province.  The year after his ouster, Dōsan raised arms at the Battle of Nagaragawa in a bid to reclaim the headship of the clan.

Allocation of licenses

In 1560, Yoshitatsu issued licenses with an official seal to lower-level officials to permit the right to travel to donate rice to the Ise Grand Shrine.  It is noted that he utilized the same format of licenses with an official seal commonly issued by sengoku daimyō during this period. 

Yoshitatsu issued many certificates for the allocation of fiefs to bushi in Mino.  These landholdings were all based on the kandaka system which equated the yield from a given fief to a standard currency known as the kan.  This offered unique attributes relative to the system of allocation utilized by sengoku daimyō and brought about the end of the traditional sōen, or manorial system, gradually allowing for a unified standard of compensation for land, taxes, and military service.