Kirihazukuri Blade Geometry: From Armor-Piercing Tanto to Wakizashi, the Practical Aesthetics of This Distinctive Cross-Section
* Image is for illustrative purposes only.Table of Contents
The "tsukuri-komi" (construction) of a Japanese sword refers to what shape the cross-section of the blade takes. In contrast to the most common shinogi-zukuri (ridge construction), kirihazukuri (cutting-edge construction) has a distinctive cross-section where the shinogi line is positioned very close to the edge, the shinogi-ji is broad, and the flat area is narrow. This construction was commonly seen in straight swords from the Kofun period through the Nara period, and was later inherited in various forms in short swords and wakizashi, as well as in naginata-naoshi swords created by reworking naginata. This article explains the structure and history of kirihazukuri, its relationship to practical use in the Nanbokucho period, comparisons with naginata-naoshi, and points to note when appreciating existing kirihazukuri swords.
Kirihazukuri—Differences in Tsukuri-komi Viewed from Cross-Section
When comparing types of tsukuri-komi by cross-section, the characteristics of kirihazukuri become clear.
| Tsukuri-komi | Position of shinogi line | Cross-sectional characteristics | Main period/use |
|---|---|---|---|
| Shinogi-zukuri | Slightly toward the spine from the center of the blade | Shinogi-ji and flat area roughly equal width. Most common | Standard for tachi and uchigatana from the Heian period onward |
| Kirihazukuri | Very close to the edge | Broad shinogi-ji and extremely narrow flat area. Close to a wedge | Straight swords of early period, some short swords and wakizashi |
| Katakiriha-zukuri | Edge-side only on one face | Asymmetrical—one side kirihazukuri, other side hiratsukuri | Short swords and wakizashi. Popular in the Edo period |
| Hiratsukuri | No shinogi line | Flat surface continues to the edge | Standard for short swords |
| Shobu-zukuri | Near the center | No yokote, shinogi line extends to the kissaki | Wakizashi and short swords |
| Uno-no-kubi-zukuri | Near the center | Spine-side flesh reduced to form a constriction like a cormorant's neck | Short swords from the Kamakura and Nanbokucho periods |
Kirihazukuri becomes wedge-shaped overall because the thickness increases sharply near the edge, making the blade angle at the tip obtuse. The design prioritizes durability resistant to chipping over sharpness, and emphasizes a way of force transmission suited to pushing cuts. For the complete range of tsukuri-komi types, see Reading tsukuri-komi in swords; for katakiriha-zukuri, see What is Katakiriha-zukuri; and for shobu-zukuri and uno-no-kubi-zukuri, see What is Shobu-zukuri and What is Uno-no-kubi-zukuri respectively.
History of Kirihazukuri—From Straight Swords to Short Swords
The history of kirihazukuri goes back before curves appeared in Japanese swords.
- Kofun period through Nara period: Most straight swords influenced by the continent were kirihazukuri. Their form can be seen in swords preserved at the Shosoin and swords excavated from kofun
- Heian period: When curved tachi were established, the mainstream of tsukuri-komi shifted to shinogi-zukuri, and kirihazukuri gradually declined
- Kamakura through Nanbokucho periods: Kirihazukuri and katakiriha-zukuri appeared again in short swords and small wakizashi. The background was the demand for sturdy blades in close combat against armor-clad opponents
- Muromachi through Edo periods: Naginata-naoshi—naginata that were polished down and remounted as swords or wakizashi—increased in number, and because their cross-sections resembled kirihazukuri, the two began to be discussed together
For straight swords of the early period, see What is Jokoto (Early Period Swords); detailed discussion of the evolution of kirihazukuri short swords by period is covered in Morphology and Era Transition of Kirihazukuri Tanto.
Practical Demands of the Nanbokucho Period and Kirihazukuri
The Nanbokucho period was an era when ōdachi and notachi were popular, yet short swords used in grappling combat were also expected to have pragmatic designs. The reasons why kirihazukuri and katakiriha-zukuri short swords were made can be explained as follows.
- Because the blade is thick and the point is obtuse, the edge is less likely to chip when thrust into gaps in armor
- The wedge-shaped cross-section transmits force easily in pushing cuts and prying motions
- With a narrow flat area, the blade resists wear from sharpening and tolerates battlefield maintenance
In other words, kirihazukuri is a tsukuri-komi that answered the practical demand of "thrusting and prying"—the same as with yoroi-toshi—through its cross-sectional form. For the relationship to yoroi-toshi, see Yoroi-toshi and Koshi-gatana; for the overall blade form of the Nanbokucho period, see Evolution of Blade Form in the Nanbokucho Period.
Comparison with Naginata-naoshi
Naginata-naoshi are swords or wakizashi made by polishing down a naginata blade and reworking the tang. Because they resemble kirihazukuri in appearance, distinguishing between the two is an important skill in appraisal.
| Point of observation | Kirihazukuri (original construction) | Naginata-naoshi |
|---|---|---|
| Shinogi line | Runs close to the edge and remains consistent to the tang | The original naginata's shinogi remains, and its position may vary midway |
| Hi (groove) | May be engraved but is integral to the construction | Naginata-specific naginata-hi (groove with curved tip) often remains |
| Spine | The spine form is consistent throughout | Traces of spine-side reduction to adjust curvature are often evident |
| Kissaki (point) | Whether a yokote exists depends on the construction | The naginata's sharply curved kissaki is shortened, and the yokote often slopes downward |
| Width and thickness | Width and thickness as designed | Because it originates from a naginata, the width is broad and the thickness is great |
| Tang | Original tang may retain a maker's signature | The tang is reworked in polishing, and signatures are often lost |
The wakizashi and short swords of naginata-naoshi retain the original naginata's characteristics. The broad width and great thickness enable "pushing cut" performance, concentrating the power that naginata possessed from the Nanbokucho through Muromachi periods into a shorter blade. The history of naginata-naoshi is covered in Naginata-naoshi (Conversion of Naginata to Wakizashi); distinguishing naginata-naoshi from ordered naginata-form wakizashi is explained in Form and Appraisal of Naginata-gata Wakizashi.
Points for Appreciating Existing Kirihazukuri Swords
When viewing kirihazukuri or naginata-naoshi swords, pay attention to the following points.
- Visualize the cross-section: In a display, you cannot view the cross-section from directly above. Read from the position of the shinogi line and the width of the shinogi-ji whether the cross-section is wedge-shaped
- Breadth of shinogi-ji: In kirihazukuri, the shinogi-ji comprises most of the blade. Observing the grain of the jigane as reflected in the shinogi-ji reveals much about the forging
- Blade angle: Because the flat area is narrow, the blade angle at the tip appears obtuse. Also check whether the blade has become thin from sharpening wear
- Form of groove: If a naginata-hi remains, naginata-naoshi is likely; if the groove is integral to the construction, it is probably original kirihazukuri
- Condition of tang: Whether the tang is original or polished provides a clue to whether it was made as kirihazukuri or reworked later
- Kissaki and yokote: The presence and position of the yokote indicate the type of construction and whether modification occurred
For wakizashi construction in general, see Complete Guide to Wakizashi Tsukuri-komi Classification; the geometric meaning of shinogi is explored in The Geometry of Shinogi.
The "Aesthetics of Practicality" Shown by Kirihazukuri
Kirihazukuri possesses an aesthetic distinct from the balanced beauty of shinogi-zukuri. The wedge-shaped cross-section, broad shinogi-ji, and obtuse blade angle all result from prioritizing "not breaking" and "transmitting force" over "razor sharpness." The tactical demands that Nanbokucho period warriors sought are literally carved into the form of the cross-section. Naginata-naoshi too is a product of practical wisdom, breathing new life into naginata that had finished their role as long-hafted weapons, waste-free and repurposed as swords. For those wishing to trace blade form changes through the ages, see also Reading the "Zukuri" of Swords.
Summary
Kirihazukuri is a wedge-shaped construction with the shinogi line positioned very close to the edge. It began with straight swords of the early period and was used again in short swords and wakizashi of the Nanbokucho period as a pragmatic design. Naginata-naoshi are modified swords retaining the original naginata's characteristics; while they possess cross-sections similar to kirihazukuri, traces of modification appear in the groove, point, and tang. By systematically checking the position of the shinogi line, the breadth of the shinogi-ji, the form of the groove, and the condition of the tang, one can decipher whether a given blade is originally kirihazukuri or a sword reborn from a naginata.
