The Capable Lord of Yoshida Castle: Sakai Tadakatsu and the Toyotomi Brothers – Unraveling Wartime Tōtōmi through Diaries

Sakai Tadakatsu, the foremost of the Tokugawa Four Heavenly Kings, governed the eastern Mikawa region for 25 years from his base at Yoshida Castle (in present-day Toyohashi City, Aichi Prefecture).

Tadakatsu was personally appointed as a mediator in difficult negotiations between Tokugawa Ieyasu and Toyotomi Hideyoshi, earning high praise from Hideyoshi himself, who called him "a capable man." What was the nature of Tadakatsu's relationship with Hideyoshi and his brother Hidenaga—the so-called "Toyotomi brothers"?

A talk event exploring the connection between Sakai Tadakatsu and the Toyotomi brothers, alongside the historical landscape of Wartime Toyohashi, will be held on Saturday, June 27, Reiwa 8, at the Toyohashi Machinaka Library.

Yoshida Castle, photographed during the Meiji era

"Branch Manager of the Tokugawa Corporation in Eastern Mikawa"

Sakai Tadakatsu was born into a family of retainers serving the Matsudaira clan, the predecessor of the Tokugawa.

He was older than Tokugawa Ieyasu and, during their youth, accompanied Ieyasu to Sunpu as a hostage of the Imagawa clan. After Imagawa Yoshimoto's defeat at the Battle of Okehazama, Ieyasu achieved independence and took control of eastern Mikawa. Tadakatsu then governed the region for 25 years from Yoshida Castle.

Tadakatsu could aptly be described as the "branch manager of the rapidly growing Tokugawa Corporation in eastern Mikawa." At the time, eastern Mikawa was home to numerous small local lords known as "kunishū," such as the Saigo, Kanzaki, and Todo clans. These kunishū were, metaphorically speaking, "strong-willed local SME CEOs (laughs)."

Tadakatsu skillfully managed relationships with these kunishū, leveraging their strength to deliver devastating blows to the renowned fierce Takeda army during the Battle of Nagashino—where he fought against Takeda Katsuyori—and in earlier battles at Yoshida Castle and Niranki Castle.

The eastern Mikawa kunishū who backed the winning side rose in status and were later elevated to daimyo or hatamoto ranks in the Edo period. As a result, they passed down the Battle of Nagashino as a "lucky war" to their descendants.

The Capable Negotiator: Sakai Tadakatsu in the Warring States Era

Tadakatsu excelled not only on the battlefield but also as a mediator between the Tokugawa and other warring daimyo. Possessing exceptional negotiation skills and enjoying deep trust from Ieyasu, he played key roles in diplomatic talks with prominent warlords such as the Uesugi, Takeda, Oda Nobunaga, and Toyotomi Hideyoshi.

He was especially praised by Hideyoshi as a "capable man," to the extent that Hideyoshi reportedly said, "Send Tadakatsu as the envoy." Tadakatsu was entrusted by Ieyasu with difficult negotiations with Hideyoshi and successfully fulfilled his mission.

The Warring States Samurai Diary: "Kachū Nikki" (The Diary of Ieyasu)

A diary written by Matsudaira Ieyasu, a native of present-day Kōta Town, Aichi Prefecture, who served under Sakai Tadakatsu and was the father of Matsudaira Tadatoshi, the third lord of Yoshida Castle. Also known as "Hihon Fukō Nikki" or "Sanshū Nikki," it is famous as a diary written by a Warring States period samurai.

It records daily events in Ieyasu's life and is a valuable historical source for understanding the activities of Tokugawa Ieyasu and Sakai Tadakatsu.

This talk event will use "Kachū Nikki" and materials held by the Toyohashi City Library to explore the historical landscape of Toyohashi during that era.

Supplement to Kachū Nikki

<Event Details>

Date: Saturday, June 27, 13:30–14:30

Venue: Toyohashi Machinaka Library

Lecturer: Okamura Tatsuo (Curator, Toyohashi City Library)

Capacity: 50 people (first-come, first-served)