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 kama's effectiveness the samurai to appropriate and modify it into a weapon of their own, the kusarigama (“chain-sickle”).
Kama are wielded in pairs, because two-handed weapons (i.e., the katana and various polearms) were the most prevalent throughout history, and these are vulnerable to Kūsankū movements. In general, one kama is used to block, parry, or trap an opponent’s weapon while the other kama makes a simultaneous counterattack.
Do not block with the blades. Kama blades are made from brittle high-carbon steels, with short tangs, and are secured with a few rivets or pins. The kama will break when the blade is struck directly. Instead, all blocks should be performed with their hardwood handles.
The kama can also be spun into a retracted position, like the sai, using the shaft along the forearm to block, and using the handle's ends for less-than-lethal strikes. Be advised that elbow strikes from this retracted position become extremely lethal.
Kama are dangerous; even experienced users 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. 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 extremely rare, and internet searches will return 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 with blunt edges and/or that “mall ninja” aesthetic which empties wallets and destroys personal credibility.
The best (and cheapest) option is to order your kama from an Asian garden store. While that sounds bizarre, the internet makes it easy; use "kama sickle" as your search term. Be aware that real kama are irresponsibly sharp, and intrinsically dangerous. You should buy two sets, and remove the edge from one set with a file or grinder. This way, you can train with safer practice weapons that model your real weapons in every way.