Ko-Aoe Naotsugi

Ko-Aoe Naotsugi was a swordsmith who flourished in the Aoe region of Bitchu Province (present-day western Okayama Prefecture) from the late Kamakura through the Nanboku-chō period, and was one of the master craftsmen of the Aoe school. The Aoe school was a group of swordsmiths originating in Bitchu Province who, influenced by both the Bizen and Yamato traditions, developed a distinctive jihada expression known as "Aoe skin." This made the school one of the most distinctive in Japanese sword history.

The defining characteristic of Naotsugi's swordmaking lies in the jihada expression unique to the Aoe school, called either "clear skin" (sumihada) or "crepe skin" (chirimenihada). Minute koitame are densely packed, with fine jiei rising throughout like mist, giving the blade's jihada a distinctive lustrous, damp appearance. This skin texture, known as "Aoe clarity," has long been praised in sword appraisal circles and is prized as a beauty unique to the Aoe school—one that other schools find nearly impossible to replicate. The hamon is primarily fine straight blade (hosozuguha) or small undulations, displaying a distinctive nie-kuchi with fine nie densely arranged along the edge. Within the hamon, one sometimes observes the style characteristic of the Aoe school where "the blade enters below the uchikaeshi," an important criterion for determining authenticity.

Naotsugi's most renowned masterpieces are several extant tachi signed with the mei "Naotsugi," some designated as Important Cultural Properties. These tachi retain the well-proportioned sugata of the late Kamakura period, with clear, beautiful jihada combined with serene straight hamon embodying the spirit of an era transitioning away from court nobility culture. The balance of blade length, curvature, and thickness also exemplifies the ideal sword form of the time, making these works valuable primary sources for studying the stylistic evolution of Japanese swords from the late Kamakura through Nanboku-chō periods.

The Aoe region of Bitchu Province where Naotsugi worked was located in present-day Kurashiki, Okayama Prefecture, and served as a strategic junction connecting the San'in and Sanyo regions. In this region, where high-quality iron sand and abundant fuel were readily available, the Aoe school developed its distinctive forging culture. As a central figure in the school, Naotsugi pioneered artistic swordmaking that consciously pursued jihada beauty, transcending mere weapon manufacture.

The Aoe school's techniques were inherited by successors such as Tsugunao, Moritsugi, and Sadatsugi, who all became accomplished swordsmiths. When compared to works by later Aoe swordsmiths, Naotsugi's pieces receive the highest praise from sword researchers for embodying the most archaic and pure Aoe aesthetic.

His most renowned signed masterpiece, the Important Cultural Property "Tachi Mei Bitchu-no-kuni Jūnin Sa-hyōe-no-jō Naotsugi-saku," is housed in the Kyoto National Museum and is noted by scholars both domestically and internationally as exemplifying the pinnacle of the Aoe school.