I. Concerning the Ninja Arts
8. Classifying Ninja
i. Rank
d. Ansatsu Senjutsu Tokushu Butai - ANBU
In every ninja village there are certain shinobi of considerable skill and discipline who answer directly to the Kage, performing the most dangerous and most sensitive missions. In the Leaf, these ninja are known as ANBU Black Ops.
The position of an ANBU is not part of the ordinary genin-chunin-jonin rankings, but rather distinctly separate from them. ANBU are not chosen so much based on individual skill as they are on mastery of the basics and understanding of the Ninja Code. ANBU are anonymous agents, so they are all taught the same techniques and fighting styles. With a few exceptions, ANBU are strongly discouraged from using techniques that are highly distinctive to them, such as original ninjutsu of their own creation, as these could be used to identify them and potentially compromise village security.
The most important thing for an ANBU is their discipline. While sentimentality or reluctance to do certain things can be forgiven in other ninja, an ANBU must willing to do anything for the village without hesitation or regret. It is not strength that makes ANBU dangerous, for many jonin and even some chunin are more powerful, but their mentality of self-sacrifice and unwavering sense of duty.
ANBU are as faceless shadows. They feel no fear and do not bleed. They are the arm of the Kage, via which he asserts his authority and maintains order in his village.
(Even the Third Hokage, a known idealist and peerless shinobi, had at times the need to make such decisions as many would consider horrible. Not everyone can be saved, and not everyone wants to be saved. There were many times when he and his predecessors had to choose between evils for the good of the village - this is the unfortunate reality of the world in which we live. -Iruka)
