This technique is simply the generic use of genjutsu as employed by Sharingan wielders. By establishing direct eye contact with the intended opponents, the user can lock them within a genjutsu of their choosing in order to achieve various effects. These effects range from inducing instantaneous, but temporary, paralysis or unconsciousness in an opponent to forcefully extracting any valuable information that they possess or controlling their actions.
Forms & Uses
Using his Sharingan, Sasuke stares at his opponent directly in the eyes and they stare back. Then a shadowy figure of himself appears before them forcing them under a genjutsu. An image resembling his Susanoo appears in front of the opponent and grasps them as it begins "assimilating" them into itself. This breaks the opponent's will. Afterwards, the opponent is left incapacitated.
Itachi is seen using an illusion that traps the victim in a dark empty space where their body is made of paper that burns from toe to head while the user is watching. The genjutsu will make it harder for the target to move properly. It bears a great resemblance to his Tsukuyomi, though it is used with the regular Sharingan. There is some dispute as to whether or not this technique was the result of a failed Tsukuyomi attempted by Itachi on Kakashi. This failure resulted from Itachi using the technique on a clone.
It is believed that Kakashi used this sort of genjutsu in the first battle against Zabuza Momochi when the Sharingan is introduced in the series. Kakashi was seemingly able to use Zabuza's techniques before Zabuza himself had the opportunity by influencing Zabuza (with his Sharingan) into using the same technique. Zabuza equates this usage of the Sharingan to hypnotism.
When Sasuke used this genjutsu he was seen covering his left eye afterwards.
Sasuke's completed version of Susanoo was first seen in this genjutsu, though as a shadowy figure before its complete début in the fight against Danzō.