永享・享徳の乱期

The Eikyō-Kyōtoku disturbances — encompassing the Eikyō Rebellion (1438–39), the Yūki War (1440–41), and the long Kyōtoku conflict (1455–83) — plunged the Kantō region into half a century of chronic warfare between the Koga Kubō (Ashikaga Shigeuji) and the Kantō Kanrei Uesugi houses (Yamanouchi and Ōgigayatsu branches). This sustained regional conflict had profound consequences for sword history. First, it created persistent demand for blades at all quality levels: high-quality commissions from powerful warlords like the Koga Kubō and Uesugi lords, and large volumes of functional 'kazuuchi' (mass-produced) swords for ordinary warriors. Second, it drove the eastward migration and local settlement of swordsmiths, particularly those working in the Sōshū末伝 (late Sōshū) lineage descended from the Jūtetsu disciples of Masamune. These smiths established workshops across Musashi, Sagami, Kazusa, Shimōsa, Kōzuke, and Shimotsuke provinces, forming the regional sword-production network that would arm Kantō warriors through the Sengoku period. The concurrent Ōnin War (1467–77) in the capital scattered Kyoto and Bizen smiths across the country, and the two simultaneous upheavals together triggered a nationwide geographic redistribution of sword-forging capacity. This diversification of regional sword culture — with each province developing its own smithing traditions — was the direct foundation for the diversity of Sengoku-period sword production. The period also witnessed the qualitative bifurcation between luxury commissions and mass production that would intensify throughout the Sengoku era.