Eiroku Era — On the Eve of Nobunaga's Ascent

The Eiroku era (1558–1570) encompasses twelve years of extraordinary historical density in Japan's Sengoku period. In 1560 (Eiroku 3), Oda Nobunaga defeated Imagawa Yoshimoto at the Battle of Okehazama; in 1568 (Eiroku 11), he entered Kyoto with Ashikaga Yoshiaki as his nominal shogun. Within this short span, the struggle for Sengoku hegemony entered a new phase, and sword culture underwent a major corresponding transformation.

The Eiroku-era sword market was dominated by mass-produced blades from Sue-Bizen and Sue-Mino. Sue-Bizen, centered on Osafune in Bizen Province, mass-produced affordable practical combat blades. The standard form was the uchigatana with blade length of 2 shaku 2 to 3 sun (approximately 67–70 cm). To meet the insatiable demand of the age of war, efficient production systems took priority over individual smith identity. Blades marked "Sukesada" and "Kiyomitsu" were supplied in great quantities throughout the nation's battlefields. In Sue-Mino, centered on Seki (present-day Seki, Gifu Prefecture), blades bearing marks such as "Kanemoto" and "Kanesada" were mass-produced, and swords from both production regions formed the primary equipment of Sengoku warlords.

From a technical perspective, what stands out in the Eiroku era is the diversification of hamon (blade pattern) styles. In addition to the gunome and chōji hamon established in the Nanboku-chō and Muromachi periods, more simplified notare and suguha were adopted for mass-produced blades. This change was not merely a decline in quality, but rather a reflection of rational design thinking that anticipated combat damage, repair, and re-polishing in actual warfare. Meanwhile, high-ranking warriors and daimyo continued to commission high-quality custom-made blades, and accomplished smiths throughout the country produced masterwork-quality pieces to individual order.

One of the most significant changes in Eiroku-era sword culture was the rapid spread of firearms (tanegashima). At the Battle of Okehazama in 1560 (Eiroku 3), Nobunaga is recorded as having employed firearm units in organized fashion (though historical sources offer various interpretations). The seeds of firearms tactics—which would develop through the Battle of Mikatagahara in 1572 (Genki 3) and culminate at the Battle of Nagashino in 1575 (Tenshō 3)—can be traced to this era. The spread of firearms did not diminish the sword's primary role; rather, it specialized and purified the sword's function in close-quarters combat. The systematization of swordsmanship techniques—drawing, striking, and counter-striking—into formal schools is a characteristic feature of this period.

Nobunaga's entry into Kyoto in 1568 (Eiroku 11) refocused the center of sword culture back toward Kyoto and the Kinai region. Nobunaga was renowned as a connoisseur of swords and showed strong interest in collecting named blades. The collection of celebrated named blades—which would later become, alongside meibutsu-gire (precious historical textiles), a cornerstone of Nobunaga's acquisitions—began in earnest at the time of his entry into Kyoto in the Eiroku era. Nobunaga's aesthetic judgment and political application of swords—gifting prized blades to forge alliances, bestowing named blades as honors for battlefield achievement—foreshadowed the "meibutsu politics" of the subsequent Toyotomi and Tokugawa periods.

The Eiroku era occupies a special position in Japanese sword history as the period of maximum political and social upheaval during the transition from late-Kotō to Keichō Shintō. The technical knowledge and experience accumulated by the smiths who lived through this era would become the foundation that gave the subsequent Momoyama and Keichō periods their distinctive vitality.