What is the Mune of a Katana Sword?

The mune designates the back part of the katana, also known as the “spike”, i.e. the back of the blade opposite the cutting edge (ha). Unlike the cutting part, the mune is not intended for slicing, but rather to ensure the weapon’s structural balance. The design of the mune is essential to provide adequate flexibility and optimal weight, making the katana both sturdy and easy to handle. The Mune is traditionally slightly curved, reinforcing the famous curvature of the katana that gives it its unrivaled aesthetics and dynamics.

Etymology

The etymology of the word “Mune” (棟) in Japanese goes back to concepts related to structure and architecture. The kanji character 棟 translates as “crest” or “ridge” and originally referred to the upper part of a structure, notably the ridge of a roof. In martial contexts, this term has been adopted to designate the non-edged part of the katana, the back of the blade that serves as the blade’s “spine”, providing stability and balance

Thus, the word Mune, in its original context as in katanas, refers to a notion of support and fundamental structure.

Different types of Mune

There are several types of mune, each influencing katana handling. The fighter’s needs often determine these variations, the tradition of the forging school, the era, and the specific use of the sword.

• Iori Mune (roof-shaped mune) or gyou no mune: This is the most common type of mune. It features an inverted V shape with a hermitage of varying height, reminiscent of a traditional Japanese roof. This structure adds rigidity to the blade while allowing a certain degree of flexibility.
• Maru Mune (rounded Mune): This version has a rounded shape. It gives the blade greater resistance to impact, but slightly reduces cutting efficiency due to a slight increase in weight.
• Hira Mune (Flat Mune): The hira mune is mainly used on lightweight blades designed for fast cutting. It enhances the blade’s aerodynamics and agility.
• Kaku-mune, or square mune: Gives the blade a strong, powerful appearance.
• Mitsu-mune (true Mune) or shinomune, has a triangular or trapezoidal structure with three distinct ridges, giving the blade added rigidity. This type of Mune is often found on ancient and traditional swords, offering the blade extra support for precise cuts. It appeared during the Heian period (794-1185) and became a central element in swordmaking, particularly in the Yamashiro-den and Soshu-den styles. This type of blade back has endured through the ages, notably the Koto and Shintō periods, and is frequently found on high-quality katanas and tantō from these traditions.

Mune function

The Mune is much more than just a part of the blade. Its shape contributes to the balance of the katana, adjusting weight and mass distribution. A thicker mune can make the sword stiffer, while a thinner mune allows greater flexibility. By absorbing shocks and vibrations during use, it protects the blade from deformation or breakage, while facilitating fluid movement during cutting strokes.

In addition to its structural role, the mune can affect the katana’s balance point, influencing handling and precision when cutting. In this way, the mune plays an essential role in the weapon’s dynamism and control.

The structural importance of the Katana Sword Mune

The mune plays a crucial role in the distribution of forces exerted on the katana during use. When the sword impacts a surface, the force is not concentrated solely on the cutting edge but is propagated through the blade to the Mune. This transfer of energy enables the katana to reduce the risk of breakage while offering a more precise cut. Without a well-balanced mune, the blade could deform or break under the repeated pressure of blows.

The Mune also helps adjust the overall weight of the sword. A thicker mune makes the katana heavier, which can be beneficial for a fighter seeking to deliver powerful strikes. Conversely, a thinner mune makes the weapon lighter, favoring speed and fluid movements.

Aesthetic

While the Mune is primarily functional, it also plays an aesthetic role in the katana’s overall appearance. Its design contributes to the weapon’s visual harmony. The gentle curvature of the mune combines with the curvature of the blade to create a coherent, balanced whole. Some mune are sometimes decorated or polished as part of the finishing process known as suriage, to enhance the sword’s beauty.

Symbolism

In Japanese culture, the Mune is often compared to the backbone of the katana, symbolizing the strength and resistance of its owner. This parallel between the sword and the soul of the swordsman is very much present in forging rituals and ceremonies. Some sword schools consider the mune to be a reflection of the warrior’s character and discipline, representing self-mastery and inner strength.

Master smiths sometimes adorned the Mune with engravings or inscriptions, such as their name or spiritual symbols, making each sword unique and carrying a personal meaning.

Mune-Uchi technique

The term Mune-uchi refers to the technique of striking an opponent with the Mune instead of the sharp side of the blade. Although rarely used in practice, this technique enabled an opponent to be neutralized without being killed, illustrating the mastery and respect for life inherent in the way of the sword.

In reality, however, the use of Mune-uchi was risky. Inverting the katana alters the center of gravity, making manipulation more difficult. Moreover, striking with the mune could cause serious injury, even death, if too much force was applied. Although often depicted in historical dramas and works of fiction, this technique is rarely mentioned in traditional samurai writings.

The Mune in the Forging Process

Mune crafting requires a high level of craftsmanship. The swordsmith called a tōshō, must carefully choose the thickness and shape of the mune according to the desired characteristics of the blade. This process is often marked by a balance between resilience and flexibility, two essential qualities for a high-performance katana. Too much thickness can make the blade stiff and unwieldy, while too thin a mune can impair the weapon’s strength.

Mune thickness and Shinogi

The thickness of the Mune (the rear, non-edged part of the katana) plays a key role in the strength and aesthetics of the blade. When a katana is examined vertically, the thickness of the mune is called Mune-zukuri.

Another key aspect of a katana’s structure is the Shinogi, the dividing line between the flat part of the blade (the Shinogi-ji) and the sloping part (the ji). These ridges, called Shinogi, help to refine the blade to improve its sharpness while reducing impact when struck. Like the mune, the Shinogi also influences the blade’s flexibility and strength. A blade with a higher Shinogi will have a thinner cross-section, which improves cutting ability but makes the blade more fragile. Another important measurement is the Shinogi-suji, which corresponds to the width or thickness of the blade between the Shinogi. A Bo-hi can also be hollowed out between the Mune and the Shinogi to lighten the blade.

Yamatoden Katanas, for example, have a Shinogi-suji much thicker than the top of the Mune. This is also the case for the “Shobu-zukuri”, “Kanmuri-otoshi zukuri” and “Unokubi-zukuri” blades. The aim is to facilitate the passage of the blade when cutting, to lighten and reinforce the strength and resilience of the material.

To check the thickness of the mune, simply hold the katana upright and watch how the ridges protrude from each side of the mune. The thickness of the mune can vary depending on where it is measured: at the base, it is generally around 7 mm, while at the tip, it is thinner, around 5 mm.

The width of the blade (from base to tip) and the thickness of the mune evolve with time and the different eras of manufacture. For example, during the Kamakura and Nanbokucho periods, blade width became more uniform from base to tip.

Finally, the balance between Shinogi height, body width, and Mune thickness influences both the visual appearance and feel of the katana when handled. The interaction between Shinogi height, Mune shape, and blade thickness affects both the overall aesthetics and performance of the katana.