Chakra Blades

A is a highly uniquely-designed trench knife. These blades are worn like brass knuckles, but each one has a sharpened zigzag "tooth" over each knuckle, and a blade coming out of one end. The knives are made from a special metal that can be infused through "chakra flow" with elemental chakra or even Yin–Yang chakra to produce added effects. According to Shikamaru, the blades are able to absorb the chakra type of the user, and become the origin of a technique, for the user.

Asuma Sarutobi coupled these knives with his taijutsu skills to have a devastating effect, such as being able to take out nine Otogakure ninja in a matter of seconds. When infused with wind-natured chakra, they can easily pierce and cut through stone and even metal. The knives' sharpness and effectiveness can also be maximised if the person has better control of their chakra as seen with how Asuma was training Sora and Naruto Uzumaki in focusing their wind chakra into their kunai. After Asuma's death, the blades come into Shikamaru Nara's possession. When infused with his shadow chakra, they can immobilise anyone whose shadow it pierces.

Trivia

 * Naruto is seen using the chakra blades in the non-canon Naruto x UT OVA.