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This technique exerts a hallucinatory effect upon the eyesight, effectively blinding the opponent. No matter how skilled an opponent may be, they are forced to wait helpless in this world of darkness, as this technique allows the user to attack unseen. Although it negates sight, it does not stop the other senses. When used in combination with Chōyumemyaku Kekkei Genkai, it has the potential to permanently blind the users target.
Despite its high level, it is a common technique among the Hō-ō Clan, who "inherited" it from the Senju Clan. In both Clans, it is one of the three (later four) techniques that a member must be able to flawlessly execute before they are seen as adults.
In the manga and anime, this technique is called by its full name, Genjutsu: Bringer-of-Darkness Technique (幻術・黒暗行の術, Genjutsu: Kokuangyo no Jutsu, Literally meaning: Illusion Technique: Bringer-of-Darkness Technique). The databook entry for this technique drops the "Genjutsu" part.