Taigen Sessai

Taigen Sessai (1496-1555) was a Zen monk and military advisor who served the Imagawa clan in the Sengoku period. As the tutor (moriyaku) to Imagawa Yoshimoto, he broadly led everything from Yoshimoto's education to the Imagawa clan's diplomatic and military strategy. He was a giant of both literary and martial excellence who, while practicing as a high-ranking monk of the Rinzai sect, demonstrated outstanding political and military genius.

Sessai was born in Suruga Province (present-day Shizuoka Prefecture), entered the Buddhist order from childhood, and trained in Zen practice. He trained at famous temples such as Kenni-ji and Myōshin-ji, and later became住持 of temples connected to the Imagawa family. He built connections with the Imagawa family during the era of Imagawa Ujichika (Yoshimoto's father) and was appointed as Yoshimoto's tutor at his birth. Thereafter, while teaching Yoshimoto Confucian learning, military arts, and etiquette, he was also deeply involved in Imagawa family administration.

Militarily, Sessai also served as one of the Imagawa clan's top leaders. At the Battle of Azukizaka (1548), as the effective commander of the Imagawa forces, he repelled Oda Nobuhide (Oda Nobunaga's father), greatly contributing to the establishment of Imagawa Yoshimoto's position. In 1554, he also became the architect of the "Kōsō-Sun Triple Alliance" with Takeda Shingen and Hōjō Ujiyasu, establishing Imagawa security on both east and west. This alliance created the foundation for Imagawa Yoshimoto to advance westward for the later Battle of Okehazama.

In the realm of Japanese swords, Sessai, though a Zen monk, had a deep understanding of swords. The relationship between Zen and bushido was close in medieval Japan, and Sessai is said to have taught his disciples the spirituality of the sword and the state of "unity of Zen and sword" (tōzen icchi) through the spirit of Zen. As a military advisor to the Imagawa family, he is said to have gathered information on swordsmiths from various regions and been involved in procuring swords for Yoshimoto's use. Also, swords associated with the Imagawa family were offered at the Zen temples where Sessai served as住持, and he is valued as a figure who embodied the cultural intersection of Zen and swords. Sessai passed away in 1555 at the age of 60, and his achievements are inscribed in history as those of the greatest meritorious retainer who supported the flourishing of Imagawa Yoshimoto from the shadows.