One of the traditional tools used by the ninja of feudal Japan is the hand claws- shuko.
Metal bands that fit over the hands and wrists which end in spikes they are used for muto-dori techniques. Times where the ninja would face a number of armed adversaries.
Also used as a form of tekko- “brass knuckles”, the iron bands added heft and weight to the various strikes (atemi) used in taijutsu.
A unique historical training tool from the feudal era of Japanese history.