Ninja weapons were drawn from a variety of sources. They used many of the standard weapons of the day, including staves, swords, knives, and chain weapons. However, as ninja were trained to travel incognito they also adapted many of the weapons that Okinawan peasants developed into weapons, so that they could travel armed but not be recognized as ninjas. Their arts also led them to devise many weapons that were specific to the tasks they needed to accomplish, and this further led to a differentiation between the tools that standard ninjas used and those used by female ninjas, called kunoichi.
Bojutsu is the martial art of using a staff weapon called bo. A bo is a wooden staff of about six feet of length and a diameter of three and a half inches, tapering towards either end. The basic purpose of the Bo was as a defensive weapon. It was perfect for parrying and blocking opponents’ strikes. However, when used offensively it allowed for long-range crushing and sweeping strikes, plus thrusts. Its tapered ends were used to strike opponents’ eyes, throat, and solar plexus. It could manage joint-locks, strikes at joints and foot sweeps, all which could stop a target without lethal force. Martial arts techniques, such as kicks and blocks, are also often combined with the weapon techniques when practicing this martial art to enhance its effectiveness.
Ninjas would sometimes use hollow bos. By flicking the staff with great speed, the ninja could launch a poison tipped dart or small knife out of the open end of it, often catching the opponent off guard.
The bo was originally a long wooden staff used for walking, herding livestock, or guiding boats. It was also laid across the shoulders and baskets or buckets were placed on either end to ease in their carrying. Bos were easily found in the wild and could also be easily improvised from a broom or fishing pole handle.
The art of fighting with a bo is Bojutsu.
A traditional Japanese weapon that consisted of a kama on a metal chain with a heavy iron weight at the other end. Attacking with the weapon usually entailed swinging the weighted chain in a large circle over one’s head, and then whipping it forward to entangle an opponent’s spear, sword, or other weapon, or immobilizing his arms or legs. This allowed the kusarigama user to easily rush forward and strike with the sickle. A kusarigama wielder might have also struck with the spinning weighted end of the chain directly, causing serious or deadly injury to his opponent while still outside the range of the opponent’s sword or spear.
Though the kusarigama is derived from a farmer’s sickle, and though the sickle was often carried as a weapon by farmers during the feudal era of Japan, it is important to note that these farmers did not carry kusarigama. Its purpose as a weapon was very obvious, so unlike a sickle, it could not be carried openly.
According to some accounts, the kusarigama was traditionally used by ninja as it is a weapon that is well-suited against swords and spears. Whether or not ninja embraced the weapon, records show that the kusarigama was extremely popular in feudal Japan, with many schools teaching it, from about the 12th to 17th Century.
The art of fighting with a kusarigama is called Kusarigamajutsu.
The naginata is a scimitar-like blade of three feet in length attached to the end of a three-foot pole shaft. It is a pole weapon that was traditionally used by soldiers and samurai, popular because it could cut and thrust from a distance. Early naginata consisted simply of a blade and shaft, a tsuba (hand guard) was added later. Double-edged blades and blades set at right angles became the most popular type.
A specific weapon of ninjas was bisen-to, a very heavy and massive naginata, able to cut and break a samurai’s armor.
During the Gempei War (1180-1185), in which the Taira clan was pitted against Minamoto no Yoritomo of the Minamoto clan, the naginata rose to a position of particularly high esteem. Cavalry battles had become more important by this time, and the naginata proved excellent at dismounting cavalry and disabling riders. The widespread adoption of the naginata as a battlefield weapon forced the introduction of sune-ate (shin guards) as a part of Japanese armor. During the Muromachi Period (1392-1573) hundreds of styles of naginata developed, but, with the arrival of firearms in 1542 began a decline. By 1600 it was relegated to a symbolic position.
The naginata, interestingly enough, was also referred to as the “woman’s spear,” because women of the Japanese military class were expected to have perfected its use by age eighteen. During the Edo Period, as the naginata became less useful for men on the battlefield, it became a symbol of the social status of women of the samurai class. A functional naginata was often a traditional part of a samurai daughter’s dowry. Although they did not typically fight as normal soldiers, women of the samurai class were expected to be capable of defending their homes while their husbands were away at war. The naginata was considered one of the weapons most suitable for women, as it allows a woman to keep a male opponent at a distance, where his greater height, weight, and upper body strength offers less of an advantage.
The art of fighting with a naginata is Naginatajutsu.
The ninja sword is often referred to a ninja-to. The ninja-to was similar to a katana, but its blade was straight and the metal was not folded. Often, they are depicted as having a straight-cut tip instead of tapering to a point. There is no historical record of ninjas having ever used these, however. It is thought that they were marketed as ninja swords to soldiers in WWII.
An actual ninja would have used a ninjaken, also known as a shinobigatana. They came in a variety of sizes, but were typically shorter than katanas. They did have straighter blades than the average sword, but were still curved. Often, ninjaken were straight bars of low-quality steel with an edge ground on to them.
The typical shinobigatana carried by a ninja would most likely have been a wakizashi or cut-down katana, fitted with a katana-length handle and placed in a katana-length saya (scabbard). This may have been used to deceive one’s opponents into miscalculating how quickly it could be drawn, allowing one to use an Iaijutsu strike faster than expected. It also disguises the weapon (that would easily identify them as a ninja) as a common sword. The extra space in the saya may also be used to store or hide other equipment or goods. The idea behind a shorter sword is that it is much easier to fight in close quarters with a shorter sword, as would be necessary for a ninja acting as an intelligence-gatherer.
A knife that was traditionally worn by samurai as a secondary weapon. However, ninjas favored the weapon because of its light weight and small size. While designed to be stabbing blades, they typically had a length of six to twelve inches that allowed for slashing actions too. Ninja tantos were of lesser quality than the samurai versions, thus allowing ninjas to use them for purposes they weren’t originally intended for, such as prying open doors, digging small ditches, or hurling.
Yari, also known as a spear, straight-headed spear, kama yari, kamayari, sickled spear, or sickle lance:
Yari is a generic term for a spear, although yari are a much higher quality than an average spear. They came in a variety of shaft and head lengths, with the longest models being used by ashigaru (foot troops) in tight formations and the shorter ones replacing the daikyu for samurai. The samurai liked yari because it is thought that while a katana could slash a man in half in his armor, slashing attacks often didn’t penetrate deeply enough to be fatal. A yari would only need to penetrate a few inches into the flesh to be deadly. Plus, yaris have a reach advantage over katanas and they were difficult to parry.
While ninjas were taught to use standard Japanese spears and lances, the specific yari that they learned was the kamayari, which was a spear blade with a crescent-shaped blade at the base. The spear point was used for lunging and stabbing, while the hook was used to snag an opponent or their weapon.
The kamayari was a difficult weapon to forge because of its blade shape, so it was often an ornamental device. Despite this, the Kumogakure Ryu ninjas developed specific techniques around the weapon in the seventeenth century. However, it is also credited with being carried by pirates on the Japanese inland sea where they could use it to board other vessels, especially if the sailor were in the water. It is claimed that at least one ninja used it to swing through trees and lift opponents off their feet while he stood on a tree branch.
The art of fighting with a yari is Sojutsu.
In the early 17th century, Japan conquered the Ryukyu Islands whose main island is Okinawa. Okinawa is located some 300 miles south of the southernmost tip of the mainland of Japan. Fearing an over throw, the emperor of Japan forced the people of Okinawa to give up all weapons. Thanks to trade, the nearness of China, as well as the Shaolin monks and nuns who helped them, the Okinawans developed a means of self-protection by using common farm implements for weapons. Most of what are now traditional ninja weapons are adapted from these Okinawan weapon-tools.
A deadly, razor sharp sickle that has a half-moon shaped blade and wooden handle. The kama was a defensive weapon that was used against sword and bo attacks. It became deadly when used as an extension of the users hands. In hand to hand fighting, the kama was used to block punches or kicks but as it does so, the sickle blade could slash deeply into the arm or leg. The techniques for the kama include any number of multiple slashing, hooking, thrusting and blocking maneuvers, executed with two kama, or nichokama. The corner of the blade to the shaft should have a groove cut into it for catching the bo and other weapons without the blade digging into and getting stuck into the attacking weapon.
The kama was a traditional farming tool used for cutting grass, weeds, and bringing in the crop.
A short, leaf-bladed knife that resembled a spearhead with a handgrip. The kunai was a ninja’s best friend. It was a stabbing and throwing weapon, a knife, a gimlet, a shovel, and even a small hammer. Some kunais even had a ring attached to the pommel, allowing a rope to be attached and giving the kunai further work as an anchor or piton.
The kunai started out as a humble gardening trowel in the late 1500s. It was used by common folk as multi-purpose gardening tools and by workers of stone and masonry. The kunai is not a knife, but something more akin to a wrecking bar. The blade was soft iron and unsharpened because the edges were used to smash plaster and wood, to dig holes and to pry. Normally only the tip would have been sharpened. The uses to which a kunai was put would have destroyed any heat-treated and sharpened tool like a knife. A ninja could work as a gardener during the day and use a kunai without raising suspicion.
Nunchaku, also known as nunchucks, nunchuks, numchucks, nun-chucks, nun-chuks, nun chucks, nun chuks, or chucks:
Traditional nunchaku is two octagonal rods connected by a cord or chain. Ideally, the rods were the length of their user’s forearms, with both rods being of equal length. The cords were just long enough to hang over their user’s wrist, with both rods comfortably pointing straight to the ground.
The original techniques involve holding the weapon in a variety of preparatory postures. Once an opponent has moved their weapon or body into close range, the nunchaku is used to strike vital spots, and apply joint locks, chokes and other control techniques. An additional advantage of nunchaku is that they effectively added to their user’s reach and as they whirled about they could be used to lash out in a strike nearly an arm’s length away.
The nunchaku wasn’t a very popular weapon. This is deduced by the lack of traditional nunchaku kata. By contrast, we currently know more than a dozen traditional staff katas. The lack of popularity for the nunchaku probably came from its low effectiveness when used against the staff or other long-reach weapons, not to mention the sword. On the other hand, one who was skilled in nunchaku usage was easily able to defeat a few opponents who were armed with knives or who were unarmed. The nunchaku was also an easy to conceal weapon, suitable for carrying everyday.
There are many alternate theories of the history of nunchaku, most of them having the origins based in Okinawa, where they were adapted from a farming tool. One theory claims they were a threshing tool used as a flail to separate rice grain from its husk, with modern nunchaku little resembling the original devices. Another theory claims that there were used for stripping bark off banana trees, while yet another claims they developed from a rattle carried by night-watchmen. However, the most credible theory is that they descended from bits used on teams of horses or oxen, known as muge. Two sticks connected by rope caught someone’s eye. A warrior swung them, pictured himself bashing an opponent’s head and nunchaku was born. Following this last theory, the handles would have been curved, rather than straight like modern models. The would have been made from a strong, flexible hardwood such as oak, loquat or pasania, and the handles would have been connected with horsehair rope.
Historically, there is no evidence that nunchaku were ever used by ninjas. Instead, in the second half of the twentieth century, films, books, and other mass media forms have indelibly placed nunchaku in the hands of ninjas so that the two are perpetually associated.
Resembling a trident, the sai was a three-pronged dagger. Its basic form was that of an unsharpened dagger, with two long, unsharpened projections (tsuba) attached to the handle. The central prong was the longest, at about sixteen inches, and it was sometimes smooth and other times octagonal. The tsuba were traditionally symmetrical.
The sai’s utility as a weapon was reflected in its distinctive shape. With skill, it could be used effectively against a long sword by trapping the sword’s blade in the sai’s tsuba. Skilled users were able to snap a caught blade with a twist of the hand. There were several different ways of wielding the sai and they were used for stabbing, slashing, punching, blocking, and even throwing. Their heavy iron construction enabled a sai to punch through armor if enough force was used.
It is believed that sais were carried three at a time. Two were used for primary weapons and the third was kept in the belt in case throwing was necessary. Sais were typically thrown at opponents using weapons with a long reach. When thrown, they had a lethal range of up to thirty feet.
The sai was originally used as a farming tool for planting rice or vegetable seeds.
A wooden baton with two handles: the first at the baton’s end and the other jutting out perpendicular to the baton and placed near where the first handle meets the baton. They resemble modern day police batons very strongly. In fact, this ancient Okinawan weapon is currently enjoying very widespread modern usage by police and security organizations in addition to being used by students of martial arts. Tonfas range from eighteen to twenty-four inches in length, with the handles being about four inches each.
The tonfa was traditionally used in pairs and were made of wood, such as red or white oak. They were used to block or parry other weapons, but they were also spun in a circular motion to thrust or strike. Additionally, by using the long portion in conjunction with the short handle, tonfas were used for arm locks or to control an opponent. When held by the handle and flipped with speed and power, the Tonfa had the same deadly potential as a baseball bat or a club, but it moved faster and was easier to control.
The tonfa was originally a wooden handle that fit into a hole on the side of a millstone used to grind rice and other grains, dating back to fifteenth century Okinawa. The tool was easily disengaged from the millstone and the peasants quickly discovered its power when it was laid across the forearm.
These were cleats that ninjas would band across the ball of their feet to gain traction on slick surfaces. In a pinch they could help a ninja climb a tree or deliver a slashing kick. Even though it is commonly thought that Ashiko were used for scaling walls, most castle walls were made of stone and were therefore too hard of a surface to gain traction. It is likely that ninjas instead sought out minor cracks and crevices for toe holds, or they used ropes and hooks to make their way up walls.
Ashiko were often used in conjunction with tekagi.
Ninjas were using flash powder long before firearms were introduced to Japan. The manufacture and application of it was a useful discipline for someone that sneaks into enemy territory to blow away a specific objective or to create havoc. All of the major ninja clans developed their own flash powder recipes and it had many clever applications.
The various containers for flash powder were egg shells, nut shells, bamboo, small bottles, and wooden boxes. Egg and nut shells were glued with either rice or wax, and often contained mixtures to create flashes of noise and light, to create clouds of smoke, or to blind a person like modern day pepper spray. Bamboo was filled with flash powder to create fragmentation mines during roadside ambushes. Small bottles were used more in the city, mainly as a noise maker, often to startle horses, or distract people. Wooden boxes were used more to attack castles or fortifications to create openings in the castle defenses.
When firearms were eventually imported into Japan, ninjas adjusted their methods and became experts in using and accurately firing with the guns. They also used different sized canons or launchers with gun powder, and they had very accurate knowledge of how to prepare and properly use such materials.
The art of manufacturing and handling flash powder is called Kayakujutsu.
Typically, fukibari are two inch needles or darts fired from a fukiya or from the mouth of a ninja. Ninjas are notorious for carrying needles in their mouths to fire at opponents. They would curl their tongues into a tube shape and spit fukibari into an enemy’s face. Alternately, they would have a small bamboo tube in their mouth and fire the fukibari from it, sometimes twelve at a time. When shot from a fukiya, fukibari could deliver all sorts of toxins into an opponent from a safely hidden location. When shot from a ninja’s mouth, fukibari were mainly aimed at an enemy’s eyes and were used to cause distractions during fights.
The art of firing fukibari from a fukiya is fukibarijutsu. The art of firing fukibari from the mouth is fukumiharijutsu. While fukiari are generally associated with ninjas, during the Edo Period some schools of jujutsu and kenjutsu taught the practice to its most advanced students.
A hollow tube used to shoot fukibari at an enemy from a distance. There were two main benefits of using a fukiya. The first is that ninjas were adept at creating and using poisons, and fukibari were often dipped in some heinous conconction before being shot at a target. The second is that using a fukiya was a relatively quiet task and therefore is didn’t threaten a ninja’s hiding place. These were excellent tools for disposing of sentries or pursuing attackers with little threat to the ninja. Plus, powders and other eye irritants were also able to be blown through a fukiya if need be.
Aside from launching darts, the blowgun could be used as a snorkel while the ninja was underwater. Since the fukiya was made of bamboo, it blended in with the reeds in the water, therefore enabling a ninja to stay submerged for hours if necessary. Since fukiya were essentially bamboo tubes, they were simple enough to disguise as flutes or canes.
A set of knives and a ring attached to opposite ends of a long cord. The cord was about twelve feet in length and was made of chain, rope, horse hair, or even women’s hair. The knife end was a small wooden handle with two knives blades protruding at ninety-degree angles, or some accounts describe it as a dagger with a hook attached. The ring was typically made of steel and had a four-inch diameter. While appearing similar to the kusarigama, the kyoketsu-shogei predates it.
Designed and used exclusively by ninjas, this weapon has several functions. The knife was used in close quarters or swung around by holding on to the ring. The cord was swung to attack with the blade or weight, snapped around feet or arms to entangle, thrown like a bola, or held while striking with the knife. Additionally, the ring could occasionally be used to improvise a way up a wall or other structure. Although rope was easier for an opponent to cut or break, it was nearly silent when used or concealed. Ninjas would conceal their kyoketsu-shogei underneath a belt or sash.
A three-foot length of chain with weights on both ends. The manrikigusari was mainly used as a defensive weapon to parry strikes from swords or staffs and to disarm or restrain opponents. When necessary it could have been used as an offensive weapon by swinging the chain and striking with the weights.
Originally designed by samurai to guard a palace without spilling blood, ninjas quickly co-opted these weapons for their effectiveness, but also because they were easy to conceal and carry.
The word metsubishi means literally “to crush the eye” and it applies to a host of ninja powders or powder-like devices that work to temporarily blind an opponent. A metsubishi was typically housed in a small container with a mouthpiece attached to one side and an opening on the other, so that the ninja could blow the contents out of the box and at a target. It is also said that metsubishi were placed into egg shells or paper containers that would be hurled at an opponent’s eyes and shatter upon impact.
Metsubishi powders contained any of a variety of substances, such as sand, spices, metal shavings, ground plants (e.g. horseradish) or seeds, or even glass shavings. While they were mostly used to blind a target, they could also place scents upon them making them easier for animals to track or they could simply contain poisons along with eye irritants.
The shinobi-zue was a staff with hidden weapons concealed within its shaft. Typically, with a twist a spring-loaded spearhead would appear on one end. However, there are tales of ninjas having shinobi-zue that would fire a projectile for a few meters, that would produce chains, or that would release blinding powders or flash or smoke bombs.
The term shinobi-zue is applied to a range of different devices, as described above. They all were basic staffs and would pass any casual inspection short of handling them. The shinobi-zue was perfect for ninjas trying to pass as wandering monks.
A small, hand-held rod used for striking an opponent’s pressure points. The shobo was only slightly longer than the width of the user’s hand. It had a ring attached to its center to place over the middle finger and used to keep the shobo in place or to rotate it into other positions. It was used for stabbing, poking, pinching, striking, smashing, and scraping and they were used either singly or in pairs. The most effective places to strike were the throat, back of the neck, bridge of the nose, and groin. There were many variations of this weapon, but all of them were simple to conceal and construct.
There are a variety of different objects lumped under the category of “shuriken,” but they are all throwing blades of some sort. The two main categories of shuriken are bo shuriken and shaken. Bo shuriken are mainly long, thin and cylindrical, with varying thicknesses and shapes (think of nails, darts, and spearheads). Shaken are made from flat plates of metal, but divide further into two groups: hira shuriken and senban shuriken. Hira shuriken are the ones most strongly associated with ninjas, as they are the ones that look like multi-pointed stars. Senban shuriken tend to look like squares or lozenges. However, since ninjas are associated with both hira and senban shuriken, we shall simply use the term shaken to refer to them categorically.
Shaken are star-shaped knives that ninjas would hurl at opponents. They are almost exclusively a ninja weapon. They are small and easy to conceal, sharp and dangerous, and silent and effective. Shaken were excellent tools to create distractions, for example they would be hurled at an opponent just outside of sword-striking distance to force a flinch or feint. They were hurled at pursuers to give the ninja time to vanish. They were thrown from ambush as a diversion or delaying tactic.
The shaken was thrown so that it spun slowly in flight. Its star shape made it so that there was no need for the thrower to consider how many rotations it would make before striking its target, thus it was perfect for hurling at both advancing and retreating foes. Its razor edges coupled with its “saw” effect, made the shaken a simple, yet effective weapon. Contrary to popular belief, shaken typically were not used with lethal force.
The actual origins of the shaken is unknown. It is known, though, that shaken were first used by ninja ryu-ha. The belief is that since the other varieties of shuriken were descended from carpentry tools, that perhaps shaken were too. It’s possible that they were inspired by the cross-shaped brackets that were found in the traditional wooden architecture of the time and from metal washers that sat under the heads of nails. These brackets and washers would have been mass produced for construction. It’s easy to imagine a person spotting these blank pieces of metal and thinking of flight and thinking of sharpening their edges. The brackets wouldn’t even be conspicuous if they were carried in the open.
The art of using shuriken is Shurikenjutsu.
These were spiked metal bands worn across the palm and attached to another metal ring worn over the wrist. Tekagi are the famous ninja climbing claws. Typically they had four sharpened spikes protruding across the palm which were used for allowing additional grip when climbing, but which could also be used as a raking weapon if needed. It is claimed that the Tokagure Ryu taught sword evasion and defensive techniques with the tekagi. It is also thought that they were used to scratch messages into surfaces for other ninjas to read.
Tekagi were often used in conjunction with ashiko.
Tessen are traditional Japanese folding fans that samurai adapted into weapons by using steel ribs in their construction. Samurai were not allowed to wear their swords in the presence of both the Emperor or the Shogun. Needing some sort of weapon, they made use of what they were allowed to carry. Ninjas liked tessen because they were just one more easily concealed weapon. When closed they could be used a clubs. When opened they could deflect arrows and darts, and they could be used for distractions and for throwing. Of course, to a ninja everything is a multi-purpose tool, so they also used tessen for signaling and they would sharpen the ribs to make a slicing weapon.
The art of fighting with tessen is tessenjutsu. Kunoichi also used tessen, but they were called sensu.
When a ninja needed to lose a pursuer, he dropped a bagful of Tetsubishi on the ground behind himself. They were small balls or four-sided diamonds of spikes that were designed so no matter how they landed one spike always pointed upwards. In an age where most people wore straw sandals, that one spike facing upward was sure to be a stinger in the sole of a foot.
The Tetsubishi had a number of uses for a ninja. First, as mentioned, they could aid in losing a pursuer by forcing them to fall or stumble. They could be lined around a camp perimeter to warn of approaching enemies. If the ninja leaped from a higher plane, they could be scattered across their landing point, thus keeping someone from making the same jump. Even though it’s not their intended use, they could be thrown in the face of an opponent. Finally, no matter what use they were seeing, they could be coated with poison.
Tetsubishi were likely made of carpentry by-products or any other small parts that were easily found.
Kunoichi (female ninjas) operated in a very different manner than traditional ninjas. They were typically posing as geisha, prostitutes, or other seductresses. They were often within very close proximity to their target and were typically there with consent. The main function of a kunoichi was to gather or spread information, but they were also trained in the arts of killing. They carried with them many different tools which would allow their escape if they needed to flee or if they needed to remove a threat.
In addition to the weapons described below, a kunoichi would have used fukibari and metsubishi while infiltrating a target’s trust. While operating as a traditional ninja, a kunoichi would have used any of the weapons on the Ninja Only Weapons list.
A form of wooden Japanese sandal that was worn with a kimono. The geta is a wooden sole with two planks (called ha, or teeth) that extend from the bottom. They attach to the foot with a fabric thong. Kunoichi would wear geta as part of their disguise and learned to use them to generate bone-crunching kicks.
A very slender dirk. Kaiken are heavily associated with kunoichi for their ability to be hidden up a sleeve or other parts of her garments in the blink of an eye.
The kakute was a simple metal ring. Some had sharpened edges and others had sharpened prongs or blades. No matter the design, they worked the same conceptually. Kakute were dipped in poison and, while a kunoichi was strangling a victim, she could penetrate their neck and deliver poison into their bloodstream. It made for a swift and quiet assassination and would occasionally leave little evidence of how the victim died. The ring could be worn reversed to conceal the prongs or blades.
A traditional Japanese umbrella. They were made of bamboo and paper as a means of keeping off the sun and rain, but eventually became considered an art object of their own. Kasas were part of a geisha’s attire and a kunoichi would have worn one as part of her disguise. When closed a kasa could be used for thrusting, striking, tripping, and locking an opponent. When opened it would provide a kunoichi a momentary shield to prepare another weapon or strike without giving her enemy notice.
Semi-circular hair combs used for decorations by geisha. They were traditionally made of wood or ivory. Kunoichi would wear kushi as part of their disguise. However, they were also quite capable of using them to rake at an opponent’s eyes and some kushi were adjusted to have sharpened teeth, permitting a hacking strike.
The Japanese equivalent of a wide sash or belt. It was part of a traditional kimono and was made of silk or cotton. Kunoichi would wear an obi as part of their disguise and learned to make it into a weapon of last resort. As a weapon it was used to constrict, entangle, and choke enemies.
These were strong, iron fingernails that were fastened on to fingertips by leather bands. They were dipped in poison and used to scratch at an opponent’s eyes.
Sensu are traditional Japanese folding fans and were oftentimes used as props in nihon buyoh (classical Japanese dancing). It was fashionable for geisha to carry sensu. Kunoichi carried sensu that had bamboo ribs, and when closed they made a good club. When opened they could deflect arrows and darts, and they could be used for distractions and for throwing. Additionally, kunoichi could use them for signaling.
Traditional ninjas also used sensu, but they were called tessen.
Fighting against pirates is no easy matter. Pirates are tough as nails. It took numerous bullets and sword slashes to bring Blackbeard to his end. There are stories of pirates with their necks cut open crawling from below decks to take revenge on a scoundrel above boards. Pirates are spontaneous. They swing from ropes, smash bottles to cut with, and flip over tables. Pirates are laden with weapons. Black Bart carried four pistols. Blackbeard carried six, plus two swords and many knives. When they lose a hand they replace it with a weapon. Pirates cheat. You’re just as likely to have a bottle smashed over your head as you are to have a monkey open a hatch at your feet. They’ll kick you in the groin or toss a grenade for you to catch. Finally, pirates are drunken rebels with a hate for organized armies, especially one of men sneaking around in black suits. Pirates detest sneaks! With their drunken machismo pirates will fight with Davey Jones himself and do a handy job of it.
So how does a ninja defeat so wily an opponent? The real trick lies in finding a weapon that works under a variety of circumstances and in a variety of environments. Ninjas never know if they’ll be engaging a rowdy army on land or a furious foe aboard ship.
Our perfect pirate-slaying ninja would carry four weapons: a naginata, a ninjaken, a kusarigama, and a pouch or two of tetsubishi.