Kunai

A staple long-range dagger-like weapon used by Ninja, the Kunai is traditionally a large triangular dart that can be modified to suit different purposes. They can be either used as daggers or throwing weapons.

Ninja Gaiden
Kunai with small timed explosives attached to them. The wielder throws the kunai, at which point the kunai is imbedded in the target and explodes a few seconds later.
 * Incendiary Shuriken (Ryu):

Kunai with small timed explosives attached to them. Similar to Ryu's varient however these kunai also possess an Iris that spins when caught by the wind, creating a destracting sound.
 * Incendiary Shuriken (Ayane):


 * Kunai with scrolls:

As Ryu traverses from area to area in Ninja Gaiden a kunai with a purple Iris attached will be thrown by Ayane into Ryu's vicinity on a wall or on the floor. The kunai will have a folded-up scroll inside the dagger and will usually offer advice, tips, or even a foreshadowing of events to come.

Trivia

 * Interestingly a type of Iris in Japan is known as Ayame, the same name as Ayane's mother.