Understanding Genjutsu
Genjutsu (幻術; Literally meaning "Illusionary Techniques") are techniques that are employed in the same fashion as ninjutsu, requiring chakra and hand seals. However, the primary difference between the two is that the effects of genjutsu are illusory; instead of attacking the victim's body, like taijutsu or ninjutsu, genjutsu techniques manipulate the flow of chakra in the victim's brain, thus causing a disruption in their senses. This is often used to create false images or to cause pain from trauma (because the body is led to believe it is in pain); however, there are plenty of other uses depending on the situation. Genjutsu can also be used to manipulate others, similar to brainwashing by feeding the victim illusive suggestions. However, there exists at least one genjutsu, Izanagi, which has the opposite effects to normal genjutsu, by changing reality to illusion and vice versa.
Genjutsu is created when a ninja extends their chakra flow through the cerebral nervous system of their opponent to control their mind's chakra, thereby affecting their five senses. Those with special abilities like the Uchiha clan's Sharingan or with high intelligence have an easier time executing and countering genjutsu, as attention to detail is key. Those under the influence of genjutsu either freeze in place or lose consciousness, depending on how capable they are in recognizing and defending against it.
Genjutsu attacks usually require a lot of skill, and, if performed incorrectly, will not work. Genjutsu is most often used by ninja with very precise chakra control and very high intelligence. Because genjutsu affects activity throughout the Prosencephalon structure of the brain, humans, dogs and other species of mammal are therefore all affected by genjutsu; however, the kikaichū, like all insects, lack such a structure to their brains, and so do not even notice it: insects are ruled almost solely by five powerful senses alone, which makes them immune to genjutsu and gives the Aburame clan an ability to detect it when nobody else can. Among genjutsu the most dangerous are those that affect the opponent with sound allowing the user to stay out of sight.
Combating Genjutsu
The first option is for the ninja to stop the flow of chakra in their body, and then apply an even stronger power to disrupt the flow of the caster's chakra; this is called Genjutsu Release (幻術解, Genjutsu Kai). This can also be done by an unaffected ninja by applying a sudden surge of chakra into the affected person. In addition, tailed beasts can break their jinchūriki out of genjutsu in a similar fashion if they have a good enough cooperation.
The second option is through intense pain not caused by the genjutsu and utilizing the resulting pain to bring their senses back in order (of the first two options, the latter seems more effective in most situations, or at least is the easiest).
The third option is accessible only to Sharingan wielders. Members of the Uchiha clan can break or see through genjutsu using their Sharingan. Breaking Tsukuyomi is possible with an ordinary Sharingan, but requires a lot of skill.
Finally, one can prevent a person from casting genjutsu using obstructive techniques like the Hidden Mist Technique to prevent one from seeing the opponent in the first place.
In spite of these methods, some forms of genjutsu like Tsukuyomi may not be broken easily, either due to the near-instant effect, or their ability to render one unconscious and paralysed altogether. In addition, one must realize that he or she is under the effects of genjutsu before attempting to break out of it. This can be done by observing the changes in one's own chakra like the chakra-sensing ability, having the ability to see through certain genjutsu, having a teammate not under the genjutsu break it for you.
Different Types of Genjutsu
Sight; The most common and sometimes the strongest too. This involves the target to acknowledge whatever part of the body/object is used in casting the genjutsu. This can range from eye to eye contact, leaves/dust capturing and ensnaring the mind in the jutsu. The moment the target acknowledges whatever is being used as the caster then the genjutsu is activated, no ifs or buts.
Sound; with the ability to alter frequencies and travel the furthest distance, sound genjutsu has been revered too as the strongest ways to ensnare someone. This gives the user the ability to fight long range and out of the way of enemy attacks while still using powerful attacks. Usually used to paralyze, lull one into sleep, hypnotize or create trauma through pain – made to feel real by the very real pain caused from high pitched noises.
Touch; caused by one sending chakra to the target through touch. This can be done through objects set beforehand, set in seals or barriers as traps as part of the defence in place, and once the target has made contact with the desired implement then the genjutsu is in place.
Smell; very rarely used to cast genjutsu but probably one of the better ways to trick someone unsuspecting or prepared for an attack via sound/touch or sight. The effects are usually harder to escape, should the target break the chakra flow the toxins used would still be in the system from entering the nose – meaning that some sort of after effect is still in play.
Taste; similar to smell and is rarely used, since the genjutsu would’ve been administered via the mouth the after affects would be harder to break – can be coupled with a medical attack for further damage.
Advanced rulings
A basic rule of thumb should be everyone following the honour code. Obviously some genjutsu, despite rank, would be more potent that others and therefore harder to break or avoid than others of the same level. Likewise any rules pre-mentioned in the administering of the genjutsu must be followed by both parties; i.e dice rolls.
No meta-knowing, to break a genjutsu one has to know one is in it – however that doesn’t mean you can just know instantly.
Obviously a Mangekyo Sharingan technique is going to be of the highest dojutsu genjutsu abilty, so even someone who is amazing at breaking genjutsu is going to be affected by it. Approach each attack as something new and fresh; don’t apply the same rule to everything.
