A Kunai is a Japanese dagger, possibly derived from the masonry trowel. Although a basic tool, in the hands of a martial arts expert, the kunai could be used as a multi-functional weapon. It's associated with the ninja, who used it to gouge holes in walls. Kunai were originally made to be farming tools but soon evolved into the weaponry they have become today. Many popular manga and ninjutsu characters use kunai as both their primary and secondary weapons.
Shuriken are commonly known in the West as throwing stars or ninja stars although they were originally designed in many different shapes. They were supplementary weapons to the sword or various other weapons in a samurai's arsenal, although they often had an important tactical effect in battle.