Kama are small sickles, used to harvest crops. Kamajustu, the art of using the sickles as a self-defense tool, is one of the hallmarks of kobudō. The many weapons bans throught history did not apply to kama, since they were required tooling for farmers. The effectiveness of the kama led the samurai to appropriate and modify it into a weapon of their own, the kusarigama (“chain-sickle”).
Historically, kama were wielded in pairs. This is because the most prevalent weapons of that era (i.e., the katana and various polearms) were two-handed weapons, which were vulnerable to Kūsankū movements. In general, one kama is used to block, parry, or trap an opponent’s weapons while the other kama makes a simultaneous counterattack.
Do not using the crook of the kama to block an incoming weapon. Kama blades are made from relatively brittle high-carbon steels, they have short tangs, and they are secured with a few rivets or pins. The kama will break when struck in that way. Instead, all blocking techniques should be performed with the handles.
The kama can also be spun into a retracted position, like the sai, using the shaft along the forearm to block, and the using the end of the handles for less-than-lethal strikes. Be advised that elbow strikes from this retracted position become extremely lethal.
Kama are dangerous; even an experienced user can incur serious or fatal injuries if their concentration were to waver. If a student is tired or distracted to any degree, they must stop kama training at once. For this reason, the kama are reserved for black belts.
We will not make an in-depth or rigorous study of kamajutsu; we will only explain how the kama is used within Goshin-Jutsu Karatedō; that is, our system’s form for this weapon. Our weapons training serves as a supplement and teaching aid to our empty-hands training, and it primarily consists of practicing the and analyzing the bunkai for the following kata:
For more information on kamajutsu, please consult Fumio Demura's Karate Weapons of Self-Defense: The Complete Edition. Alternately, you can get an electronic copy of his earlier book, Kama: Karate Weapon of Self-Defense. (Avoid looking for used print copies of this book; they are rare, and internet searches will just bring up thousands of different Kama Sutra translations.) Kama: Weapon Art of Okinawa, by Toshishiro Obata is also a useful reference. (Though this might seem like a cop-out, no one can do a decent job of teaching kamajutsu without blatantly plagiarizing these books.)
Tips on selecting kama
Kama are a standard item in martial arts supply stores, websites, and catalogs. However, most of these kama are stage props without an edge, and/or they have that “mall ninja” aesthetic that empties wallets and destroys personal credibility.
The best (and cheapest) option is to order kama from an Asian garden store. While that sounds bizarre, the internet makes it easy; use "kama sickle" as your search term. Real kama are irresponsibly sharp; they are intrinsically dangerous. It is best to buy two sets, and remove the edge from one set with a file or grinder. This way, you can safely train with practice weapons that are, in every way, like real weapons.