Blue fire powder (青火粉, Aobiko) is a special substance that creates a large explosion when exposed to water. It was accidentally discovered by the Kumanoi clan of the Howling Wolf Village when they were trying to create a medicine that would grant eternal youth. To increase the explosive power of that substance, it was mixed with potassium nitrate, sulphur, and charcoal, thus creating blue fire powder. Use of blue fire powder can significantly level the playing field, allowing weak or even non-shinobi to compete with shinobi of superior training and numbers, as when the the Howling Wolf Village defeated Amegakure. Sale of blue fire powder brought great wealth to the Kumanoi clan and the rest of the Howling Wolf Village, enabling the village to cease being a hidden village.
One of the more common ways to use blue fire powder is to load it into "cylinders". When the cylinders are blown into, moisture in the breath ignites the powder, shooting whatever projectile the cylinder is loaded with; smaller, personal-sized cylinders are loaded with small stones. There are also larger, military-grade cylinders that are loaded with actual rocks, but these require actual water to fire. Land mines can be created, whereby the powder is moistened just enough to detonate when stepped on by an adult. In Kakashi Hiden, the Ryūha Armament Alliance hides blue fire powder in parachutes: when anyone using them passes through clouds, the explosives are primed and then detonate upon landfall.