Bunkai (分解?), literally meaning “analysis” or “disassembly”, is a term used in Japanese martial arts referring to the application of fighting techniques extracted from the moves of a kata.
Bunkai is usually performed with a partner or a group of partners which execute predefined attacks, and the student performing the kata responds with defenses, counterattacks, or other actions, based on a part of the kata. This allows the student in the middle to understand what the movements in kata are meant to accomplish. It may also illustrate how to improve technique by adjusting distances, time moves properly, and adapt a technique depending on the size of an opponent.
Some kata have another layer of application that is taught using an Oyo Bunkai, an “application of the kata in ways other than the standard bunkai.” Different practitioners will learn or discover alternative applications, but the bunkai, like the kata, varies based on the style and the teacher.
A single kata may be broken into anywhere from a few to a few dozen applications, and the same sequence of kata moves may sometimes be interpreted in different ways resulting in several bunkai. Some martial arts require students to perform bunkai for promotion.
Bunkai can be obvious or elusive depending on the technique in question, the moves preceding and following it, and the individual practitioner. There are usually many stages of depth of comprehension of bunkai only reached through the passage of time. The terms toridai and himitsu are used to refer to techniques not readily seen to the casual observer and hidden techniques within kata.
The following video shows Craig demonstrating Heian Shodan (the first Kata everyone learns) and then Sensei Davis showing some Bunkai from the Kata.