Agni Kai is a traditional firebender duel that is centuries old. It is a fight for one's honor and is won only when one opponent burns the other. Any firebender may participate; male or female can be challenged. Fire Lords can also be challenged, but that rarely happens, because most Fire Lords are among the most powerful firebenders in the world.

If one person has a dispute with another person, he or she may challenge the other person to an Agni Kai. If the challenge is accepted, the two combatants move to either an official dueling area or whatever open area is available, such as a parade ground or plaza. The ceremonial opening begins with the two combatants opposite each other with their backs turned. The combatants stand, face each other, shed their shoulder garment, which was used only in formal Agni Kai, and begin the duel as soon as the gong sounds. In a proper fire duel, both combatants (if male) fight with a bare torso.