Gishu

A Gishu (義手, Gishu) is a type of artificial limb developed by Kyoka Shimura. Gishu were designed in order to allow a shinobi to continue active duty despite a loss of an arm.

Overview
A Gishu is a highly complicated piece of equipment that has to be custom made for each individual. The arm itself is made of an alloy that can be infused with chakra. The insides of the armpiece contain multiple wire-like structures that are connected to the user's chakra pathway system, allowing them some semblance of movement with the fingers. However, because the Gishu only made it to the prototype phase, complex finger movement is limited, preventing the user of the majority of hand seals.

Kotarō's Gishu replaced his left arm and contained a hidden compartment by removing the hand, allowing him a small scroll within. This scroll has a fire technique sealed within, allowing his Gishu to act as a flamethrower. His Gishu was also equipped with a sheath for his tantō, allowing easy access. After finding out that his Gishu couldn't be used to make hand signs, the fingers were equipped with sharpened nails, forming a makeshift claw instead.

Trivia

 * Because Kyoka kept the designs of this tool encoded, nobody knew how to create them after her assassination. This prevented the tool from becoming widespread after its initial creation.
 * The design notes were later decoded by Kotarō Shimura, but for reasons unknown, he did not share his knowledge with the rest of the Konoha.