Sakakibara Yasumasa

Sakakibara Yasumasa (1548–1606) was a warrior and daimyō from Mikawa Province (present-day Aichi Prefecture), renowned as one of the "Four Heavenly Kings of Tokugawa" (Sakai Tadatsugu, Honda Tadakatsu, Sakakibara Yasumasa, and Ii Naomasa). Excelling in strategic intelligence, he served Tokugawa Ieyasu as an outstanding general of both literary and martial accomplishment. After the Battle of Sekigahara, he became lord of the Tatebayashi Domain in Kōzuke with 100,000 koku, contributing to the governance of the eastern provinces in the early Edo period.

Yasumasa was born in Tenbun 17 (1548) as the second son of Sakakibara Nagamasa, a local landowner in Mikawa Province. From boyhood he served the Matsudaira family (later the Tokugawa) as a page and gained Ieyasu's trust. He participated in important battles including the Battle of Anegawa in Genki 1 (1570) and the Battle of Nagashino in Tenshō 3 (1575), accumulating military achievements. Particularly at the Battle of Nagashino, he distinguished himself as a vanguard captain of the main force, and his military prowess became renowned.

At the Battle of Komaki and Nagakute in Tenshō 12 (1584), Yasumasa engaged the main forces of Toyotomi Hideyoshi's army while skillfully developing strategic maneuvers. In this battle, Yasumasa became famous for the anecdote where he distributed provocative documents challenging Hideyoshi's forces throughout the region, earning Hideyoshi's anger to the point where a bounty was placed on his head. At the Battle of Sekigahara in Keichō 5 (1600), he joined the Eastern Army on the Tokugawa side, and was awarded 100,000 koku in Tatebayashi, Kōzuke after the battle. He died at Tatebayashi Castle in Keichō 11 (1606) at the age of 59.

In the realm of Japanese swords, Yasumasa was a warrior who held swords sacred as a matter of warrior pride. Inheriting the tradition of Mikawa warriors, he passed down swords received from Ieyasu as family treasures. Several blades associated with the Tokugawa shogunal family were handed down in the Sakakibara family, and the sword collection formed during the Tatebayashi Domain period influenced the sword culture of future generations. As a general who excelled in military strategy, his tactical writings and military texts have also been regarded as important materials for later research in military science. He is highly regarded as a Sengoku warrior who embodied the spirit of Japanese swords and the samurai, as an outstanding general of both literary and martial accomplishment.