Types of Short Swords Explained in Detail: Differences Between Aikuchi, Yoroidoshi, Koshigatana, Kougai, and Kaiken

What Are Short Swords? — Blade Length Standards and Definitions

In the classification of Japanese swords, the term "short sword" (tantou) generally refers to swords with a blade length (ha-chou) of less than one shaku (approximately 30.3 cm). However, in reality, the term "short sword" is an umbrella designation for multiple formats and forms, each with its own distinct name and characteristics.

This article provides a detailed explanation of each format under the umbrella of "short swords" from the perspectives of structure, use, and historical background.

Aikuchi — Representative Unguarded Self-Defense Sword

Definition and Structure

Aikuchi is a representative form of short sword without a hand guard (tsuba). The name "aikuchi" derives from the fact that the boundary between the blade and hilt connects "as if the mouths came together" without a guard. The joining point between blade and hilt has no guard, and the overall appearance is streamlined with the mouth and hand end fitting snugly together.

Era and Use

Aikuchi became particularly widespread in the Edo period as a self-defense tool for samurai women and upper-class townspeople. Lacking a guard, it has less striking power, but is unobtrusive when carried in one's garment and allows for quick unsheathing. In the inner quarters (women's residential areas) of samurai residences, it was prized as an indispensable self-defense tool.

Decorative Value

In addition to their function as self-defense tools, many aikuchi feature high decorative value. Aikuchi adorned with gold inlay (chinkin), lacquer painting (makie), or mother-of-pearl inlay (raden) were treasured as wedding furnishings and gifts. Fine pieces with elaborate decoration are particularly highly valued in collections.

Yoroidoshi — Practical Weapon Aimed at Armor Gaps

Definition and Structure

Yoroidoshi is a short sword designed specifically to pierce through gaps in armor. It is characterized by a cross-section with a triangular or near-square diamond shape, narrow blade width, and high rigidity. Many examples have double edges (moroba—blades on both sides).

Technical Background

While conventional swords primarily use slashing with thin, sharp blades, yoroidoshi is designed with piercing as the top priority. It is a sword highly specialized for the extremely practical purpose of thrusting into gaps in the armor's iron plating—under the arms, between the neck and helmet, and through eye holes—to kill the enemy.

Historical Background

Yoroidoshi was most needed during the Southern and Northern Courts through the Sengoku period (14th–16th centuries), when armor and helmets were highly developed. In this era when samurai took to the battlefield wearing full armor such as dou-maru, o-yoroi, and touseigusoku, demand arose for weapons capable of penetrating armor. From the Edo period onward, as armor wearing became more ceremonial, practical demand declined, but its value as a collectible remains high today.

Evaluation in the Modern Market

The sharp decline after the Edo period can be attributed to the increasing formalization of armor wearing as well as the loss of market viability for a "thrust-only" function in a time of peace. Because so few survive, they tend to be highly valued for their rarity in the modern sword market, and complete examples that retain a clear diamond cross-section command particularly high prices.

Koshigatana — Everyday Worn Sword of the Muromachi and Sengoku Periods

Definition and Use

Koshigatana is a sword with a blade length between that of a short sword and a long short sword (approximately one to one-and-a-half shaku), worn at the hip for everyday use. In current classification, it occupies the boundary region between "short sword" and "long short sword."

Historical Position

During the Muromachi period, the practice of wearing a "daisho"—a pair consisting of a long sword and a short sword—became widespread, but during the transition period before this culture became established, the koshigatana functioned as the everyday worn sword of samurai. The very name "koshigatana" reflects a function-descriptive naming of "a sword worn at the hip," marking it as a product of an era when function took priority over form.

Kougai — A Unique Combination of Military Equipment and Practical Tool

Definition and Structure

Kougai is an elongated metal rod shaped like a hair-styling tool (kougai), collected in pairs with a small blade (kozuka) in the sheath's side. Its function as a sword is supplementary; it functioned primarily as a multipurpose portable item used for arranging hair and serving as a practical tool.

Relationship to Swords

Kougai is not a standalone "sword" but is housed in a sheath as an attachment to a long short sword or regular sword. However, since it is classified as sword equipment, in the context of sword collections it is often traded as "a complete set with kougai." The presence or absence of a kougai becomes an important evaluation point in assessing the completeness of the overall mounting.

Era and Decoration

Kougai underwent decorative development during the Azuchi-Momoyama through Edo periods. Kougai with exquisite metal carving executed by skilled metalworkers are today highly valued as important artworks constituting the "mounting" (koshirae) of swords.

Kaiken — Self-Defense Sword Carried by Women

Definition and Characteristics

Kaiken is a short sword for self-defense that women carry concealed in their garment, also called "sleeve sword" (fukorogata sword). Most are in the aikuchi (unguarded) style, with elegant exteriors finished in white sheath (shirasaya) or decorated with lacquer painting and mother-of-pearl inlay.

Wedding and Kaiken

In samurai society, kaiken was one of the bride's "wedding trousseau" items. Kaiken used in wedding ceremonies such as the "Three Cups Ceremony" (sankon no gi) held symbolic meaning as markers of the bride's chastity and resolve. Even today, in Japan's traditional Shinto wedding ceremonies, brides in white wedding attire (shiromuku) continue the custom of carrying kaiken, and this cultural tradition remains alive.

As Preparation for Ritual Suicide

Beyond its role as wedding furnishing, kaiken also served as preparation for ritual suicide (jigai), by which samurai women could end their lives if captured by enemies. Surviving examples of kaiken with hilts finished thin and short to prevent the hand from slipping when cutting the carotid artery testify to practical self-defense design philosophy concealed beneath the decoration.

Size

The typical kaiken has a blade length of approximately five to eight sun (15–24 cm), making it relatively small even among short swords. It is designed to fit compactly from hilt to sheath as an integrated whole, with a portability-friendly compact form as its defining characteristic.

Gomabashi and Nakiri — Ceremonial and Practical Short Swords

These rank lower as "swords" but represent the broader base of Japanese sword culture.

Gomabashi: A ceremonial short-sword-shaped tool used in Buddhist fire ritual (goma). It has minimal edge and carries primarily religious rather than practical cutting function. It is strongly characterized as a Buddhist ritual object and is positioned as a religious symbol borrowing the form of a sword.

Nakiri: A short-sword-shaped blade tool developed for culinary use. While not a "Japanese sword" in the strict sense, it is an important example demonstrating how Japanese blacksmithing techniques were applied to household cutlery.

Comparison Table of Each Type

Conclusion — The Diversity of Short Swords Reflecting Layers of Japanese Culture

Each form of short sword is a product of Japanese blade culture optimized for its respective era, social class, and purpose. Rather than simply defining them as "swords with blade length under one shaku," understanding the historical context and function of each form brings into sharper focus the profound depth of Japanese swordsmanship.

For collectors and enthusiasts, grasping the characteristics of each form is the first step toward broadening one's appreciation. In particular, aikuchi and kaiken have high artistic value, with many masterpieces featuring refined mountings still in existence. TOUKENZA carefully selects and features short swords of each type, allowing you to view them thoroughly online through photographs and detailed explanations.