Tsukuyomi


 * Debut (Anime): Episode 82
 * Debut (Manga): Chapter 142

Named after the Shinto Moon god, Tsukuyomi is one of the most powerful Genjutsu in existence. It is unique to the Uchiha clan and only those with the Mangekyo Sharingan can perform it. When executed, the jutsu traps the target in an illusionary world that is completely controlled by the user. While it only takes a few seconds to complete in the real world, the user can make it seem as if days have passed for the target. Depending on the user's whim, they can either torture their target for days on end, or make them relive a traumatic event over and over. When the jutsu ends the resultant psychological trauma will render the target unable to fight for a while, and possibly suffer a complete mental breakdown. An example of this is Kakashi Hatake, who had to be hospitalized for quite some time after Itachi performed the Tsukuyomi on him.

While the illusion is never the same twice, some elements always remain. The first and foremost similarity is the red moon, which hangs in the sky of each illusion. The moon, in turn, casts a red light throughout the illusion, giving the background a blood-red appearance while the figures within the illusion are in a grayscale inverted color.

Because the Sharingan is the main factor in executing this jutsu, eye contact is required. When he used it on Sasuke, however, Itachi seemed to force Sasuke to open his eyes. Sasuke had both eyes closed prior to Itachi's activation of the technique, but opened them in shock as Itachi used the technique. Alternatively, Itachi may have simply caused Sasuke enough pain to open his eyes, or Sasuke did so by himself, despite how unwise such an action was.

Such a powerful technique is not without its disadvantages, however. Due to of the complexity of the illusion and the quickness with which it is executed, an enormous amount of chakra is necessary to perform it. Though Kakashi says that Tsukuyomi cannot be escaped, Sasuke has been able to break out of Tsukuyomi by using his own Sharingan.

Influence
Pulling from the ancient Japanese myth of Amaterasu, Tsukuyomi, and Susano'o, where when Izanagi washed his face after escaping the underworld his right eye became Tsukuyomi, the Moon god.