A Hachiwari (鉢割), also erroneously spelled as Hachiwara, was a rare sidearm carried by the samurai in medieval Japan, which could be used for parrying. During the early period (before 1600), samurai would typically carry a Tachi (longsword) along with a Tantō (short sword).
Later, the combination of a Katana and Wakizashi became more common. There are records indicating that in some cases, Hachiwari were carried instead of these sidearms.
Overview
The blade of the Hachiwari had a square cross-section and was forged with a hook just below the hilt. The blade was concave and tapered towards the tip, which could be pointed or slightly rounded.
The hilt typically featured a small round or oval guard element. It was made of wood, wrapped with Japanese lacquer (Urushi) or woven silk cord (Tsuka-ito).
The hilt could be slightly curved or straight, and it had a rounded or flat pommel. There were also all-metal versions. The scabbards were usually made of wood, coated with lacquer, or wrapped with strips of rattan or bamboo.
Hachiwari displayed in museums typically have a blade length of approximately one Shaku (about 30.3 cm), similar to a Tantō. The mountings, including the grip and scabbard (Saya), often resemble a Shoto or Tantō externally.
Due to climatic conditions, Japanese weapons were constructed with the grip and scabbard fitted tightly to protect the blade from corrosion, as the steel was not rust-resistant.
The Hachiwari served as a parrying weapon. With its blade, it was possible to intercept the opponent's weapon, hold it firmly with the hook, and break it.
Similar sidearms are known in the European context as a left-hand dagger or sword-breaker. With different shapes, deployable blades, or a saw-toothed back, a rapier or sword could be "caught" and blocked through a twisting motion to gain an advantage in combat.
The translation "helmet-breaker" may be misleading, as it would require immense force to break open or even dent a Kabuto (helmet) of Yoroi (Japanese armor). Moreover, it would be impractical since Japanese Kabuto did not have a fully enclosed visor.