Kōei-Jōwa Period — The Apex of Nanbokuchō Long Tachi

The Nanbokuchō Civil War and the Explosion of Sword Demand

The Kōei-Jōwa years (1342–1350) represent a period when the Nanbokuchō civil war, which intensified following the death of Emperor Go-Daigo in 1339, unfolded on a nationwide scale. The large-scale battles waged between the Northern Court government led by Ashikaga Takauji and the Southern Court led by Emperor Go-Murakami generated unprecedented levels of weapon demand. In particular, great tachi (ōdachi) and great naginata (ōnaginata) were actively forged as they proved effective in mass combat.

In response to warrior demands, smiths produced exceptionally long tachi with blade lengths exceeding 90 centimeters, and some reaching as much as 150 centimeters. These tachi were produced not only for practical use but also as votive swords (hōnōtō) dedicated to shrines and temples. The majority of surviving Nanbokuchō-period votive swords date from this time, and they testify to the level of forging technique of that era.

Intense Competition Among the Traditions and the Apex of Technical Achievement

This era witnessed the most intense competition among the four great sword traditions—Bizen, Yamashiro, Sōshū, and Yamato.

The Bizen tradition smiths (Okayama), centered around Osafune, established large-scale production systems and supplied long tachi in great quantities. Masters such as Kanemitsu and Nagayoshi reached full maturity during this period, producing supreme tachi characterized by elegant hamon featuring notare interwoven with chōji and refined ji-hada.

The Sōshū tradition (Kamakura) was led by Sadamune, who inherited Masamune's legacy, creating tachi with abundantly nie-laden, turbulent hamon and deep ji-nie. In Yamashiro, the disciples of Rai Kunishun were active, while in Yamato, schools including the Tegai and Taima also participated in the production of long blades.

The Grand Expression of Hamon and Ji-hada

The most striking aesthetic characteristic of Kōei-Jōwa-period swords is the dynamic expression of hamon. Based on notare, many examples feature large chōji-midare (clove-pattern temper) surging like ocean waves, with abundant nie and nioi throughout. The ji-hada is characterized by flowing itame with running ji-nie, creating a full and rich texture, with the entire long blade constituting a complete work of art in itself.

The blade's curve tends toward saki-zori (tip-heavy curve), with the long blade providing both battlefield utility and visual grandeur. These tachi have been highly valued by later generations as "Nanbokuchō-period works," and many surviving examples are designated Important Cultural Properties or National Treasures.

Influence on Later Eras

The sword culture of the Kōei-Jōwa period reached a zenith in the subsequent Enbun era (1356–1361), then transitioned through the upheavals of the Ōnin War (1467–) to the age of the practical uchigatana. However, the ideal of powerful, grand sword beauty established in this period remained a touchstone for later smiths, becoming one of the primary aesthetic standards that scholars of the Edo period most valued as the "beauty of the sword."