What is the Tōsu? — A Form of the Japanese Sword's "Ancestor"

The "tōsu" is a general term for small blades with blade lengths of approximately 10cm to 30cm or less. The term derives from the Chinese "dāozi," and the concept and physical objects transmitted from the continent before the Nara period took root in Japan.

In Japan, during the Nara period (710–784), under the ritsuryō system, the tōsu was officially approved as a carried item that aristocrats and officials were permitted to wear. While the tachi was a large sword for military purposes, the tōsu became an essential item for scholars and aristocrats as an everyday small blade. It was a practical tool used for diverse everyday purposes: scraping paper and wooden tablets for writing, cutting ingredients during meals, and tailoring clothing.

Regarding the relationship between the tōsu and Japanese swords (tachi and uchigatana), it is more accurate to understand the tōsu as "a parallel, distinctive blade culture" rather than "the ancestor of the Japanese sword." While the Japanese sword developed as a long, curved, single-edged weapon, the tōsu underwent its own unique development as a more practical and decorative small blade.

Tōsu in the Shōsō-in — Masterworks of the Nara Period

The most important primary source in tōsu research is the collection of tōsu housed in the treasure repository of the Shōsō-in at Tōdai-ji in Nara. The Shōsō-in houses many items associated with Emperor Shōmu (701–756) of the Nara period, among which are several tōsu.

The tōsu in the Shōsō-in collection are diverse, ranging from lavish works with iron blades decorated with gold, silver, and inlay to practical, simple pieces. One particularly noteworthy work is a court tōsu contemporary with decorative pieces featuring gold and silver flat designs. It demonstrates the process of "Japanization" wherein Japanese metalworkers adapted continental (Tang) craft techniques.

One reason the tōsu in the Shōsō-in remain well-preserved today is that the distinctive architectural style of the azekura-style storehouse with cypress bark roofing stabilizes temperature and humidity, inhibiting metal corrosion. These tōsu, which have survived for nearly 1,300 years, are first-rate sources for understanding the level of metalworking technology in the Nara period.

Tōsu Culture of the Heian Period — The Fusion of Court and Buddhism

Entering the Heian period (784–1185), the tōsu underwent unique development in both court and Buddhist culture.

Court tōsu: The tōsu worn by Heian aristocrats became increasingly decorative. They took on the character of crafted artworks that transcended purely utilitarian items, decorated with gemstones such as gold, silver, lapis lazuli, and crystal, and fitted with maki-e (lacquered) wooden scabbards. The tōsu that functioned as a small version of the "kaiken"—a short blade for self-defense carried by female aristocrats—was regarded as part of a woman's attire.

Tōsu in Buddhist temples: The tōsu played an important role in temples as a tool for making and repairing Buddhist ritual implements and for scripture copying. The tōsu possessed by high priests also carried religious significance, and in some cases, the bestowal of a tōsu from master to disciple became a symbol of the transmission of the dharma lineage.

Samurai tōsu: As the samurai class rose in the late Heian period, warriors wore the tōsu alongside the tachi. The samurai's tōsu was not purely decorative; rather, it had a strong practical character, designed for outdoor utility such as food preparation and cutting rope.

Tōsu of the Kamakura to Muromachi Periods — Integration with Warrior Culture

From the Kamakura period (1185–1333) onward, the tōsu underwent transformation as it was incorporated into samurai culture.

As an accessory to the formal armor of the samurai—the ōyoroi and dōmaru—the tōsu was worn alongside the koshigatana and koshizashi. In particular, the short blade called "koshigatana" (15–30cm) inherited the functions of the tōsu while becoming integrated into the daily life of warriors.

The renowned Kamakura-period swordsmith Awatagunchi Yoshimitsu is known as a master of the tantō, and it is said that his workshop also produced small blades equivalent to the tōsu. The samurai demand for tōsu expanded the range of works produced by master swordsmiths.

During the Muromachi period, tōsu-lineage blades such as the "kogatana" and "wakizashi" diversified, each establishing its own category. The term tōsu gradually took on the connotation of "court-style, classical small blade," while "kogatana" and "koshigatana" became dominant in everyday usage within samurai society.

The Contemporary Position of the Tōsu — Antique Markets and Cultural Properties

In modern times, the tōsu maintains a presence in multiple contexts.

Tōsu as cultural property: Ancient and medieval tōsu housed in the Shōsō-in and museums throughout Japan are protected as National Treasures and Important Cultural Properties. These cultural properties are highly valued by researchers and cultural heritage professionals as resources that exemplify the entirety of ancient and medieval metalworking, woodworking, and decorative arts.

Circulation in antique markets: Tōsu produced from the Edo period onward—particularly practical tōsu used as craftsman's tools and farm implements—circulate in antique and used goods markets. Because these fall outside the Japanese sword registration system, they can be bought and sold more freely than Japanese swords. Among sword and blade collectors, many enthusiasts collect tōsu and kogatana alongside Japanese swords.

Production by modern swordsmiths: Among contemporary swordsmiths, some craftsmen produce tōsu and kogatana in addition to Japanese swords (tachi and uchigatana). Because the tōsu requires less production time and material cost than Japanese swords, they are produced as entry-level works or as technical display pieces for craftsmen. The tōsu are sometimes featured in NHK traditional crafts documentaries and sword exhibitions, and their existence is becoming increasingly recognized by the general public.

Though the tōsu tends to be overshadowed by the Japanese sword, it is a form of Japanese blade culture that has endured for over 1,300 years from the Nara period to the present day, and it is an important presence that complements Japanese sword culture. To understand the "principal swords" of the tachi, uchigatana, and wakizashi, one cannot overlook the cultural history of the tōsu, the "supporting blade."