Nanbokucho Sword Morphology: Transitional Blade Forms from Enbun-Joji to Post-Oei Contraction

Sword Forms of the Nanboku-chō Period—The "Greatest Period of Transformation" in Japanese Sword History

The Nanboku-chō period (1336–1392) was an era of the most dramatic transformation in the formal history of the Japanese sword. Swords from this period, known as "Nanboku-chō-sugata" (the Nanboku-chō form), became an important indicator for dating swords.

The direction of change was primarily characterized by "upsizing": the blade became longer and larger, the kissaki (tip) became elongated, and the width of the blade expanded. This trend was embodied in the era of ōdachi and nodachi, and the form typical of "the Enbunn–Jōji period (around 1356–1369)" most distinctly exemplified these characteristics.

Why did swords become so large? The prolonged conflicts of the Nanboku-chō period created a social backdrop for increased demand for more powerful weapons. Additionally, the increased emphasis on foot combat (kakchikusa) was influential. Rather than being wielded on horseback, large swords and blades that were raised and swung with both hands by foot soldiers proved effective.

Formal Characteristics of Enbun-sugata—The Peak of Upsizing

In dating Japanese swords, the term "Enbun-sugata" is used. It refers to the form typical of the Enbunn–Jōji period (around 1356–1370), representing the golden age of Nanboku-chō swords.

Formally, the following characteristics stand out:

Elongation of blade length: Examples of tachi with blade lengths exceeding 80–90 cm become more common. Among ōdachi and nodachi, examples with blade lengths of 120 cm and more existed (though most surviving examples were shortened by "suriagé" (shortening by regrinding) in later periods).

Ō-kissaki: The "ō-kissaki" (large kissaki), with the kissaki becoming elongated, is one of the greatest characteristics of the Nanboku-chō period. Many examples have kissaki lengths of 2.5–4.0 cm or more, reaching two to three times the length of the inokubi-kissaki (approximately 1.0–1.5 cm) typical of mid-Kamakura swords. The shape of the kissaki is described as "ō-kissaki with a chū-kissaki (medium point) extending," with the point sharp and prolonged.

Expansion of blade width: The width near the handle (motohaba) expanded to approximately 3.4–4.0 cm. The width near the tip (sakihaba) also became relatively wider along with the enlargement of the kissaki, with the ratio of sakihaba to motohaba rising to approximately 70–80% (a significant increase from 55–65% in early Kamakura). This is a sword form with "small fumigomi"—minimal tapering toward the point—creating a solid, weighty impression.

Thickness (kasane): Some examples have kasane (thickness at the handle) reaching 0.8–1.0 cm or more, resulting in a blade with considerable mass.

The "Revival" of Koshi-zori—Characteristics of Curvature in the Nanboku-chō Period

Regarding the curvature, there was a retrograde shift: from the "chū-zori" (medium curve) established in mid-Kamakura, a trend toward "koshi-zori" (lower curve) strengthened again during the Nanboku-chō period.

This is interpreted as a return to koshi-zori for use in foot combat. Unlike the koshi-zori of the Heian period, which aimed for "ease of drawing while mounted," the koshi-zori of the Nanboku-chō period may have corresponded to a style of "carrying large swords over one's back while walking" (ōdachi were often worn on the back).

The Emergence of Enbun Uchigatana—The Dawn of Uchigatana in the Nanboku-chō Period

While the Nanboku-chō period was an era dominated by ōdachi, it was also during this time that the origins of uchigatana first appeared.

The uchigatana is shorter overall than the tachi (blade length approximately 60–70 cm) and is carried inserted into the waistband with the blade facing upward ("sashikomi"). It contrasts with the tachi, which is suspended with the blade facing downward.

From the late Nanboku-chō period into the early Muromachi period, practical uchigatana began to develop alongside large tachi. The spread of uchigatana became the foundation for the later transition to "uchigatana predominance" during the Muromachi–Edo periods.

The Shortening of the Ōei–Eisho Period—A Shift from Upsizing

With the end of the Nanboku-chō conflicts and the stabilization of rule under the Muromachi Shogunate during the Ōei–Eisho period (1394–1441), sword forms changed rapidly.

Large swords underwent "suriagé" (shortening by regrinding the nakago to reduce overall length). Most surviving Nanboku-chō tachi have lost their original full length due to suriagé. Swords that have undergone suriagé are called "suriagé-mono," and in dating, the important task of estimating the "original form before suriagé" becomes essential.

Formally:

• Blade length reduced to approximately 75 cm
• Kissaki reduced from ō-kissaki toward chū-kissaki and shō-kissaki (expressed as "kissaki becoming blunt")
• Blade width also showed a reduction trend to approximately 3.0–3.4 cm near the handle

This reduction was not merely "deterioration" but adaptation to new combat tactics of the Muromachi period (emphasizing mobility in close-quarters foot combat).

Characteristics of Jigane and Hamon in the Nanboku-chō Period

Beyond mere form, jigane and hamon also displayed distinctive trends during the Nanboku-chō period.

Jigane: Coarser grain, with ōitame and ōmokume mixed in, became more common. This reflected both an increase in forging volume (massive demand for large swords) and technical exchange between various production centers (the spread of sōshū-den influence).

Hamon: "Hiro-suguha" and "enlargement of irregular hamon patterns" were notable. In particular, bold hamon patterns such as "gunom-midare," "dai-gunom," and "hitatsura" developed during the Nanboku-chō period. Hitatsura (a hamon pattern that appears as if the entire blade were hardened) emerged as a characteristic technique of the Nanboku-chō period as a result of sōshū-den influence spreading throughout the country.

Conclusion—Were Nanboku-chō Swords a "Transitional Period" or a "Peak"?

It is possible to view the sword forms of the Nanboku-chō period as a "transitional phase from Kamakura to Muromachi," but this is insufficient. The Nanboku-chō sword form—with its ō-kissaki, broad blade width, and enlarged proportions—represented a distinctive peak with its own completeness, and the "reduction (shukutai)" in the Muromachi period onward was not a decline but a different type of optimization.

In the authentication of surviving unsigned Nanboku-chō blades (without a master swordsmith's signature), reading comprehensively the formal characteristics of the period—ō-kissaki, broad blade width, koshi-zori, ōitame jigane, and bold hamon—becomes key to correctly evaluating them as "Nanboku-chō period swords."

The circumstances by which swordsmiths from various regions dispersed during the Nanboku-chō conflicts and techniques from Bizen, Yamashiro, and Sōshū spread throughout the country are covered in Dispersal of Nanboku-chō Swordsmiths. Understanding Nanboku-chō swords from both perspectives—formal change and school transmission—yields a more three-dimensional understanding.