RE: The Naruversity
So I came up with a theory about how the basic abilities of the Sharingan work. I think it's pretty elegant, as it divides the powers up into six distinct ones, three related to the "eye of insight" and three for the "eye of hypnosis", with two unlocked at each developmental stage.
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The Sharingan is a powerful doujutsu belonging to the Uchiha clan. To awaken this doujutsu, one must experience a powerful emotional condition with regards to a person precious to them - this emotion can be positive, driven by a desire to protect or reunite with a loved one, but more often, per the clan's primary occupation as shinobi, it is negative, brought on by stress or loss. When this powerful emotion is first experienced the brain releases a special form of chakra that affects the optic nerves, transforming the eyes into Sharingan; for that reason the Sharingan is described as an "eye that reflects the heart". Unlike the Byakagun, only a relatively small number of Uchiha ever awaken their bloodline.
When first awakened each Sharingan usually will have only one tomoe, although those with particularly powerful chakra may immediately gain two tomoe in one or each of their eyes. Through training and continued use the Sharingan will develop a second tomoe and then, upon full maturation, a third.
As with any doujutsu, Sharingan can be transplanted into non-Uchiha, although they will not be able to deactivate the Sharingan and its use has a greater chakra demand for them than for an Uchiha. For these reasons, non-Uchiha tend to cover their Sharingan when they aren't using it in order to decrease the amount of visual information it needs to process and therefore reduce it's chakra usage as much as possible. Sharingan that originate from the same Uchiha are still linked to some extent even when wielded by separate users, at times enabling those users to see the same things.
The Sharingan has six separate abilities which can be broadly classified into two categories, called the "Eye of Insight" and the "Eye of Hypnotism." The abilities of the Eye of Insight relate to the physical perception of the world around oneself, while the abilities of the Eye of Hypnotism relate to the spiritual ability to perceive and utilize chakra; particularly, yin-based chakra. The powers of the Eye of Insight will always be active as long as the Sharingan itself is active, however, the powers of the Eye of Hypnotism must be consciously accessed by focusing additional chakra to the eyes.
The Sharingan has three stages of development, each of which causes the gaining of another tomoe and the unlocking of two new powers upon being reached.
Stage One (aka one tomoe unlocked): The most basic form of the Sharingan has two fundamental powers.
Clarity of Perception: The first level of the Eye of Insight. The user's brain is able to process vastly more visual information than a normal human. They see everything around them in perfect detail, from the smallest twitch of a person's muscles to individual grains of sand on a beach. The user can see much farther than normal, as well as see much smaller objects in greater detail than normally possible. They are also able to perceive and follow extremely fast moving objects that would appear as just a blur to a normal person.
If pushed to a level beyond the power of most human beings (such as by activating Orochimaru's cursed seal) this perception can extend to the microscopic level and can even mimic the Byakugan by penetrating through solid objects for a very short distance, allowing one to perceive their own body's cells.
Another benefit of this enhanced clarity is the ability to see through almost any non-Sharingan based visual genjutsu. Because the user can see the world in far greater detail and with far greater focus, they will easily detect even the smallest irregularity or flaw in the illusion which a normal person, including the creator of the genjutsu, would overlook. This makes it far easier to dilute the effects of the genjutsu until it's harmless or to outright dispel it. Only someone who has the Sharingan themselves can possibly craft a visual illusion with high enough fidelity to fool another Sharingan user.
Perception of Chakra: The first level of the Eye of Hypnosis. The user is able to see chakra energy as different colors. This allows them to see through most clone jutsu and detect those using chakra to hide or disguise themselves. This perception even penetrates through solid objects for some distance, allowing the user to discover chakra-charged people and objects (such as chakra-molding ninja or ninjutsu-based landmines) hidden underground or behind walls.
This ability also gives the user an incredible defense against any normal kind of genjutsu, including those that aren't visual based, because they can see the chakra "anchor" of any area-based genjutsu as well as the chakra of a targeted genjutsu as it travels to and enters their own body. This foreknowledge ensures that a ninja actively focusing chakra to their Sharingan can almost never be surprised by an illusion, giving them time to fortify their chakra system to resist the incoming genjutsu and to better prepare a counter for it once they are ensnared.
Stage Two (two tomoe unlocked): The previously mentioned two fundamental powers gain new applications.
Mimicry: The second level of the Eye of Insight. The user is now able to instantly memorize any physical movement they witness that is compatible with their body structure. This allows the user to easily learn any type of taijutsu they witness, as well as read another person's lips, or copy another person's writing just by watching and mimicking the movements of their pencil. Any kind of physical skill can be quickly learned in this way, from playing an instrument to operating complicated machinery.
Perception of Chakra Flow: The second level of the Eye of Hypnosis. The user can now not only perceive chakra, but also perceive the way it flows throughout the human body. This allows the user to detect irregularities in the chakra flow of others, such as being under the influence of a genjutsu. This also greatly aids in the learning and mastery of genjutsu, as the user is able to directly see exactly how their genjutsu affects the flow of chakra in the brain of another person.
When used together properly, these two powers can be used to effectively copy and learn any jutsu the user is able to clearly witness being performed. By memorizing another's handseals and watching the flow of chakra throughout their body, the user can gain an incredible understanding of the mechanics of their jutsu. If the user also meets all the requirements of the jutsu (chakra control is up to par, body is strong enough, nature transformation is already known, etc) they may even be able to immediately perform the jutsu themself.
While in theory the user can learn any jutsu this way, in practice it usually only works for basic, lower ranked jutsu. This is because most ninja will eventually reach a level of skill which allows them to "drop" some or even all of the handseals from their favorite jutsu, instead performing the required shape and nature transformations internally through pure willpower. In fact, many higher ranked jutsu have such long and complicated strings of handseals that the ability to perform many of those seals internally is practically required in order to use them in combat. Copying such jutsu is significantly more difficult, as the user must be knowledgeable enough to deduce what handseals were dropped, and where in the sequence they were dropped, simply from observing the chakra flow. Using the Sharingan to copy a complicated A-rank jutsu performed entirely without seals, such as the Rasengan, would be almost as difficult as attempting the learn it the normal way.
Level 3 (three tomoe): The final two abilities of the Sharingan are unlocked.
Prediction: The final level of the Eye of Insight. The Sharingan can now use it's ability to read and copy body language of other people to predict their movements, giving the user an incredible advantage in combat. To the user, this ability is experienced within the mind's eye as a "shadow" of the other person moving a short distance ahead of their real body. To other people, it can seem like a form of precognition (and in fact, the Uchiha clan has long encouraged this misunderstanding of their bloodline as a form of propaganda). While powerful, this prediction is not perfect; if the opponent is able to move their body in ways that are unnatural, or to suppress the normal tells of their body language and move in ways that are highly erratic and seemingly random, then this prediction can be thwarted. This prediction is also less effective the faster the opponent is able to move; the less time the Sharingan has to calculate their movements, the shorter and less accurate its predictions will be. The prediction will similarly be reduced if the opponent hides or otherwise obscures their body language, such as by wearing a mask and thick, loose clothing.
Chakra Projection: The final level of the Eye of Hypnosis. The Sharingan is now able to project a thin stream of yin chakra directly from the user's pupil, which travels along their line of sight. If the user makes direct eye contact with another person this "chakra beam" will pass through their pupil and directly into their brain. This allows the user to subtly manipulate the thoughts and actions of another person by implanting suggestions in their mind which they will believe to be their own ideas (so long as those ideas don't strongly deviate from their normal thoughts and behavior). In combination with the mimicry and prediction powers of the Sharingan the user can even fool another person into believing they can see the future, by suggesting actions and words to the other person and then completing them first and finishing their sentences.
When fully mastered, this power can also be used to project a unique genjutsu (called "Genjutsu: Sharingan") directly into another person's brain, without using handseals or providing any other tell to alert them to it. As the genjutsu travels extremely quickly, bypasses most of the body's normal defenses and usually hits the target completely unexpectedly, the effects can be devastatingly effective to a normal person, and can even be effective against another Sharingan user who would be able to resist any other genjutsu. This genjutsu is also incredibly versatile, taking many forms and serving many purposes: Inducing instantaneous unconsciousness in the target; forceful extraction of any information the target possesses; relaying of memories to the target; removing genjutsu placed on the target by others; suppressing of a tailed beast's chakra within the target; even controlling the target's actions. The Uchiha Clan has even been known to control the Nine-Tailed Kyuubi with this amazing genjutsu.
