It's not a straight blade...
When looking at a ‘ninja’ sword (ninja-to) there are many misconceptions – the first being the whole straight blade issue. If you take the premise that the ninja or shinobi was principally an intelligence agent, saboteur and only on the rarest of occasions an assassin, then the idea of having a sword that is so different from the rest of the population becomes very unlikely. The ninja wanted to pass unnoticed and be overlooked, so when he had to carry one he would choose a sword that resembled all others.
The principle katana shape of the period of the ninja’s main activities was curved, to varying degrees, and about 28 – 30 inches long – again depending on several factors. Therefore when looking at what is generally regarded as the ‘normal’ ninja-to we see a curved blade of about 1 shaku 6 sun to 1 shaku 8 sun (that’s 19 inches to 21 ½ inches) in length, sheathed in a scabbard of normal length. Having a longer scabbard than blade leaves a void at the end, which is used for different purposes. It can store papers (intelligence gathering), blinding powder (metsubushi), or other small items.
The other stereotype is the tsuba (guard). Along with the straight blade it has been thought the tsuba was a square guard (kyokaku tsuba), which when looked at from the same point of view as the blade geometry doesn’t make sense at all. The tsuba was either circular or of the four petal design that was popular at the time. In this way from the outside it looks like a regular katana, but when drawn can be used in tighter confines and at closer range. Another feature was a very long saego (cord) that was used in many ways, from tying up people, to climbing aids, to securing loads. There is a whole art called saego no nanajutsu which translates as the seven arts of the saego. It doesn’t mean literally seven ways of using it but is more a number representing misfortune – so translates as using the rope in times of misfortune.
Aside from this ‘normal’ ninja-to there are other variants. There was a shikorogatana which was a regular length katana blade with a saw tooth edge (apart from the last 2 – 3 inches). It was used in dragging cuts that caused massive tissue and internal damage, quite differently to the way a regular katana is used. There were battlefield katana called daito which was 3 shaku 2 sun (38 inches) used in mass battle situations, but also hidden in long grass in openings as a very sharp trap. Another blade that was used comes back to the ideal of being hidden again. This is the shikomizue or sword staff. The principle of hiding blades in staves is present in many cultures, and the ninja were no exception. They would use the stick as a walking aid to complete disabled or elderly disguises. When attacked they would use the body of the stick as a primary defence and the hidden blade to surprise and finish them off. They would also have tricks such as hiding blades in the handles to cut at opponents grabbing at swords and to enable escapes.
The ninja-to was worn mostly in the belt on the left hip or carried in the hand. The image of the ninja with a sword across his back is again mostly a fictional one. They may have temporarily strapped it like this, for climbing walls or rock faces for instance, but it would be a hindrance to wear it like this continuously, impeding rolling and other forms of escape. There is a technique to draw the ninja-to over the right shoulder called kage no itto, or shadow draw, which was used when going around objects or people to surprise an opponent.
The method of using the ninja-to both includes using it in the scabbard as well as drawn. In the scabbard it’s used much like a sword staff or shikomizue, utilising the tsuba to control arms, strike and disarm the opponent. When drawing the ninja-to there are several methods for releasing it from the scabbard. The traditional way is to use the thumb of the left hand to push the top of the tsuba, and as such is a fairly obvious sign that the sword is about to be drawn. The other methods include using the index finger to release the blade, using the knuckle of the left thumb on the inside of the tsuba, securing the scabbard against the body with the left arm, and turning the body so the left hand can grasp the far end of the scabbard in a hidden manner.
In a situation where you face off against an opponent and both draw to cut, the advantage of the shorter blade is that it clears the scabbard first and therefore can cut sooner. One technique is to draw moving slightly off line and cutting to the wrist of the opponent. This will either remove the hand from the sword (at the wrist) or, if armour is worn, will allow an entry point to lock up the limbs with the blade and fell the opponent.
The style of blade use differs from what may be seen in kendo, where the ninja-to can be used at close quarters as well as at a distance. In close quarter combat the blade ties the opponent and moves them off balance and the cutting action is supported by the whole body pushing through the target. When used in a more open style the distance cuts are done with the last inch of the blade, cutting to vital points (tendons, hamstrings, joints and the neck).
The ninja-to is used in conjunction with other weapons such as metsubushi (blinding powder), kunai (a heavy entrenching tool), shuriken and others. At the last the ninja could throw the ninja-to at the opponents, cast shuriken and use metsubushi powder hidden in the scabbard to create opportunities for escape and evasion.