Kunai

Foam kunai made for cosplay :)

Kunai (クナイ), like shuriken, are one of the most common tools used by shinobi. It is a black dagger — about the length of one's hand — with a handle wrapped in bandages and a ring-like pommel. While usually kept in a shinobi's weapon pouch, they can also be kept on spring-loaded wires up the user's sleeve.

Kunai generally are designed for thrusting and stabbing, but can be thrown as a projectile as well. Using it as ranged weapon, shinobi can attach an explosive tag to the blade, causing it to detonate when it reaches near its target. This use of the weapon is known as an explosive kunai (起爆クナイ, kibaku kunai). Kunai can also be empowered with chakra, allowing them to be capable of cutting through solid wood and stone.

Naruto
Twelve years before the start of the series, the ninja village of Konohagakure was attacked by the Nine-Tailed Demon Fox. The village was only saved from complete destruction by the actions of Konoha's leader, the Fourth Hokage, who sacrificed his life to seal the Nine-Tails into a newborn: Naruto Uzumaki. Orphaned by the attack, Naruto grew up shunned by most of the villagers, who hated and feared him because of the Nine-Tails trapped within him. Unaware of the monster he contained, Naruto longed for acknowledgment, and so vowed to one day become the greatest Hokage the village had ever seen. (from Narutopedia)(from Narutopedia)