If there is a ‘ninja sword’ is there a ‘ninja knife’? Well the closest that comes to it is the Kunai. Although to call it a knife would be a misnomer. The kunai was an entrenching tool, a climbing aid, rope anchor and many other practical tools before it was used for a weapon. Unlike the popularised Naruto and Manga imagery it wasn’t primarily a thrown weapon, although it could be thrown as a last resort. The literal translation of Kunai comes from the two parts it is made up of: Ku meaning death and nai meaning not to or negative. So the Kunai is meant to be used in a way that doesn’t take life, and the techniques reflect that premise. However it doesn’t mean you can’t break things with it.
It came in many shapes and sizes, from small thin ones used to lever locks and pry open small containers; to middle sized ones used to wedge doors, windows and used as climbing pitons; to large ones used as rope anchors, digging tools and climbing aids.
The design could be said to resemble a leaf shape, and it was predominantly made from iron, to give it weight. There were variations in the principle design, some would have saw edges for instance. An average sized one would be between 12 and 18 inches with a pierced or ring pommel. The ring enable a secure grip and allowed for rope to be attached. The 'blade' itself was usually blunt (aside from the afore mentioned sawtooth versions) as it was intended to dig into hard earth or structures. However the point was sharp and supported to reduce the risk of breakage.
It is used as a hidden weapon and carried concealed to some extent. The idea being that most of the ninja’s equipment had to be carried easily on the body, so as not to impede the ability to run, climb, roll and generally move. Also when produced from a place of concealment the surprise factor would create openings and advantages in combat. Some of the more commonly used places for carry are inside the kyahan or the tekko, (leg and forearm wraps) and in the belt. With the lack of cutting edge it is quite safe to carry in these places and can be drawn while moving without being obvious. They also reinforce those areas to help deflect blows from edged weapons.
The stances (kamae) used are from Kukinshinden Ryu. There are five waza or kata limked directly to the kunai called Juppo Sessho no waza. As with all waza and kata they are there to show principles, not a 'real' fight. This enables the kunai to be deployed in a great variety of ways, only restricted by the insights gained by the end user.
The five waza are called:
Kiri no Hito Ha
Rakka
Mizu Tori
Gorin Kudaki
Mawari Dori
Each waza employs the either the flat or edge of the kunai to break grip or balance, and the point to pierce the opponents defence. It is usually shown against weapons (katana) but can be used against unarmed opponents as well.
The use of the kunai isn’t limited to these techniques, but they are more specific for it. It can be used in many other ways from wrist locks, strikes, chokes, throws (of the opponent) and so on. As with most things in the Bujinkan, the dynamics used in taijutsu (unarmed) techniques is reflected whenever a weapon is used with accommodation made for the characteristics of the weapon.
The kunai’s use as an entrenching tool usually meant it was needed for escaping through locked doors, windows and wall climbing so the ninja would try to hang on to it – literally! If, as a last resort the kunai was thrown, the weight and balance of the weapon (as well as its lack of cutting edge) would mean that it would most likely knock an opponent over, rather than stick in. If the ninja had to throw weapons they were more likely to use shuriken than kunai.
To see a modern version of this, surprisingly a review of gardening implements brings us this, which could be used as a kunai in many ways. Note the sawtooth edge, the availability of string. It lacks something in weight, but that could be compensated for.