The Sharingan has an ability called the Saimingan, or hypnotic eye ability. This ability is what enables the Sharingan to cast genjutsu, and it is from this ability that the genjutsu Moonreader was born, more commonly called Tsukuyomi. The Tsukuyomi is considered to be the best genjutsu of Itachi's Kaleidoscope Sharingan.
In the physical world, people live bound by restrictions such as time, gravity, and space, and how they exert their abilities in these restrictions separates the victorious from the defeated. The Tsukuyomi is an ocular genjutsu that gives it's user the ability to exert control over these very limitations within the dreamscape, as if they were a god. It can be used to conjure any sort of world; Madara Uchiha's Project Tsuki no Me has him creating a dreamscape where the world is at total peace and prosperity, with him reigning as king. This genjutsu is called Everlasting Moonreader [Mugen Tsukuyomi], and requires him to call the moon. On the other hand, Tsukuyomi was a notorious weapon of Itachi Uchiha. As such, it is said to represent the world of the mind and darkness. Along with Amaterasu, it is a technique that must be awakened in order to attain mastery of the Kaleidoscope Sharingan beyond it's two eyes. It is a genjutsu of such strength that it was only believed to be vulnerable to another Uchiha member bearing the Sharingan.
The Tsukuyomi mainly differs with other genjutsu in that it's an ocular genjutsu, requiring the victim to look into the eyes of the user in order to take effect. The Tsukuyomi gives the victim phantom experiences such as being tortured for several days, while the user who does torturing, is not susceptible to these experiences. Thus one of the most common traits of Tsukuyomi is the ability of the user to exert control over how the victim perceives the length of the genjutsu, and the events of the dreamscape. With the double-whammy of a genjutsu that affects the mind, and can be freely modified to the user's liking, Tsukuyomi is often able to incapacitate it's victims.This control also allows the genjutsu to be completely harmless.
Thus the genjutsu is not limited to merely torturing victims, as it is essentially a genjutsu that gives the user free reign over the senses of the victim, as they have total control over the dreamscape. During his battle with Danzo, Sasuke appeared to cast Tsukuyomi over him, creating the perception of a world where his ocular jutsu Izanagi had never ended, when in reality it would not protect him.
Depending on the pain threshold of the target and the genjutsu's intensity, they can recover from the bad experiencse of the genjutsu, and it can also be broken by a partner. It was at one point used without explicit mention of the user's control over any traits, appearing to be a different genjutsu altogether until it was defeated.
- ↑ Naruto Databook 2, page 252
- ↑ Naruto chapter 389, page 1
- ↑ Naruto chapter 142, page 17
- ↑ Naruto chapter 475, page 15
- ↑ Naruto chapter 467, page 17
- ↑ Naruto chapter 510, page 7
- ↑ Naruto chapter 549, page 17
- ↑ Naruto Databook 3, page 274
- ↑ Naruto chapter 142, page 17
- ↑ Naruto chapter 257, page 4
- ↑ Naruto chapter 478, page 3
- ↑ Naruto chapter 142, page 18
- ↑ Naruto chapter 148, page 13
- ↑ Naruto chapter 388, page 13
- ↑ Naruto chapter 585, page 13
- ↑ Naruto chapter 480, page 6
- ↑ Naruto chapter 224, page 17
- ↑ Naruto chapter 388, page 9