Large Odachi and Nodachi of the Nanboku-chō Period: Formation and Use of Large Swords Born in a Time of Upheaval

Building Swords of the Nanboku-chō Upheaval and the Rise of Large Blades

From the Kemmu Restoration (1333) to the reunification of the North and South courts (1392), spanning approximately 60 years, the Japanese archipelago was placed in an unprecedented state of civil war. The conflict over the imperial succession split between the South and North courts dissolved the old manorial system and became an impetus for regional samurai groups to independently organize their military forces. This historical demand generated a highly unusual group of large swords in the history of Japanese blades.

While swords of the late Kamakura period were dominated by tachi with blade lengths around two shaku three sun (approximately 70 cm), the Nanboku-chō period saw the mass production of "odachi" with blade lengths exceeding three shaku (approximately 90 cm), and even "nodachi" extending beyond four shaku. This sudden increase in size is inseparably linked to a tactical transformation from mounted combat to infantry mass formation warfare.

Morphological Characteristics of Odachi and Nodachi

The odachi of the Nanboku-chō period exhibit several morphological indicators. First, regarding curvature, the sori developed in the late Heian period declined, with a tendency toward emphasized mid-curvature and tip curvature extending from the ridge line toward the spine. This shape enhances operability when wielding a long blade and enables thrusting techniques with the tip.

While shinogi-zukuri construction remains dominant, swords with broad blade widths and sturdy flat sides become prominent. A small ratio between base and tip widths (fukura drop) and the enlargement of the kissaki called dai-kissaki are known features of the Nanboku-chō style.

Nodachi can reach blade lengths of four shaku five sun (approximately 136 cm) or more, and function more as a specialized striking and sweeping weapon brought to the battlefield rather than as a personal weapon carried by an individual. Most existing nodachi were shortened through suriage polishing in later periods, and complete examples retaining their original full length are extremely rare from a cultural property perspective.

Battlefield Deployment and the Factors Behind Enlargement

The main battlefields of the Nanboku-chō civil war saw an increase in infantry combat such as mountain fortress attacks, night raids, and routs, rather than mounted frontal cavalry confrontations. Infantry soldiers are said to have adopted the use of odachi as a substitute for long-shafted spears and naginata. Specifically, they were effective for tripping mounted warriors to the ground and then striking them down, as well as for sweeping strikes during group mass assaults.

Furthermore, the practice of presenting swords to shrines flourished during the Nanboku-chō period, and odachi were also produced as dedicatory offerings to Shinto shrines and Buddhist temples. Odachi forged as symbols of divine power rather than as practical combat blades are still transmitted in great numbers at Ōyamatsumi Shrine and Kasuga Taisha, and many are designated as Important Cultural Properties and National Treasures.

Factors beyond tactics contributed to the enlargement. During the Nanboku-chō period, the protective power of o-yoroi heavy armor was strengthened, and in response to the armor's hardening, heavy-bladed swords emphasizing striking force and shattering power were required. This demand technically drove the elongation of blade length and the expansion of blade width.

Notable smiths representing the Nanboku-chō period include Sadamune (貞宗) and Gō no Yoshihiro (郷義弘) of Sōshū. Sadamune is said to have been a student of Masamune and forged robust odachi that inherited the essence of the Sōshū tradition. Gō no Yoshihiro left very few authentic extant works, and the pieces designated as National Treasures and Important Cultural Properties are called "coveted masterpieces" in sword-collecting circles. The Rai School (来派) of Yamashiro—including Rai Kunishun, Rai Kunimitsu, and Rai Kunitsugu—produced Nanboku-chō odachi with their school's characteristic soft ground steel and gentle hamon, while the Aoe School (青江派) of Bingo and Bizen was distinguished by their unique dark-tinted steel color (sumihada).

Representative Extant Examples and Authentication Points

A representative example of an extant Nanboku-chō odachi is an odachi by Bizen Osafune Kanemitsu (備前長船兼光). Kanemitsu is one of the representative smiths of the Nanboku-chō period, characterized by large kissaki, robust blade body, and the small chōji hamon distinctive of the Bizen tradition. He also produced examples with wide suguha hamon influenced by the Sōshū tradition, featuring kinsuji and inazuma patterns.

The main authentication checkpoints are as follows:

Ground steel: During the Nanboku-chō period, the influence of the Sōshū tradition increased examples with mixed large itame patterns. In the Bizen tradition, small itame mixed with mokume is the norm, but examples with clearly visible midare-utsuri are highly valued.

Hamon: Broad hamon patterns such as gunome-ran and large chōji that emphasize robustness are considered characteristic of the Nanboku-chō period. In the Sōshū tradition, intense hitatsura-style hardening is observed.

Tang (nakago): It is important to confirm the presence and extent of suriage polishing. When signatures have been removed, age estimation is conducted through examination of file marks on the tang, the position of the mekugi-ana, and rust conditions.

Examples from the Yamato and Yamashiro traditions also exhibit characteristics unique to Nanboku-chō odachi. The ground steel of the Yamato tradition (Nara school) is characterized by dense masame patterns, and the hamon consists mainly of suguha or small ranged patterns with an elegant style lacking the intense activity seen in the Sōshū tradition. The Yamashiro tradition (Rai School style) typically features dense steel with small itame and minimal skin patterns, with hamon characterized primarily by small ranged patterns in a gentle nioi finish, maintaining the quality of the edge even on long-bladed swords.

Signed odachi are especially highly valued in authentication. Since the Nanboku-chō period saw significant loss of signatures through suriage, signed examples retaining the original maker's signature on the tang become the sole reliable primary source for confirming the manufacturing location, smith, and period. Signed Nanboku-chō odachi tend to receive the highest ratings in assessments by the Society for Preservation of Japanese Art Swords (NBTHK), and command significantly higher market valuations compared to unsigned polished examples.

Relationship to the Five Traditions: The Influence the Nanboku-chō Period Exerted on Smiths

The Nanboku-chō period was an era in which the Sōshū tradition, among the five major traditions of Japanese sword-making (Yamashiro, Yamato, Bizen, Sōshū, and Mino), exerted particularly broad influence throughout the nation. The style established by Masamune and his followers in Sōshū (present-day Kanagawa Prefecture)—"large itame in ground steel, hitatsura in hamon, and intense activity"—resonated with the demand of the turbulent period for "stronger and larger swords," prompting smiths throughout the nation to eagerly imitate this technique.

The Osafune School of Bizen also absorbed the Sōshū tradition while establishing its own odachi style, and the "Bizen-Sōshū eclectic works" of this period receive high evaluation in modern authentication.

Suriage Polishing and Cultural Property Protection

As mentioned above, most nodachi and odachi underwent suriage polishing for practical use by the Edo period, reducing blade length to approximately two shaku three sun. In this process, signatures were often lost, and many examples survive as "unsigned" or "heavily polished unsigned" pieces.

From a cultural property protection perspective, extant unpolished Nanboku-chō odachi are considered first-class materials for viewing and research. While museum holdings and shrine-dedicated swords are often impossible to own privately, polished examples with registration certificates that have passed into private hands can be traded on the legitimate sword market. Odachi retaining the morphological characteristics of the Nanboku-chō period are highly valued among collectors, and the presence or absence of an authentication certificate (assessment certificate from the Society for Preservation of Japanese Art Swords) directly affects auction and purchase prices.

The challenge that the turbulent Nanboku-chō period imposed upon blade smiths—this gave birth to the odachi and nodachi, the largest category in sword history, whose surviving examples continue to stand as testimony to Japan's samurai culture down to the present day.