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A technique where chakra kneaded inside the body is converted into fire and expelled from the mouth either as a massive orb of roaring flame or as a continuous flame-thrower. The scope of the attack is altered by controlling the volume of chakra that is mustered. The released flames will engulf their target, and leave a crater in the ground's surface.
The Uchiha clan uses this technique as a "coming of age" rite, and as such, is a common and favoured technique amongst them.[1]
Trivia
According to Kakashi Hatake, this technique was originally created by the Uchiha clan, becoming one of their favoured moves at which they became very adept.[2]
While in the manga this technique is portrayed to be unique to the Uchiha clan, the anime has portrayed it as a common Fire Release technique used by several non-Uchiha.
During his battle with Kakashi, Naruto, Sakura and Chiyo, Itachi was seen using the hand seals: Boar, Horse, and Tiger to create this technique.[3]