Byakugan

The is the kekkei genkai that originated from the Ōtsutsuki Clan, and later inherited by their distant descendants, the Hyūga Clan. It is regarded as one of the "Three Great Dōjutsu", the others being the Sharingan and the Rinnegan.

Overview
This dōjutsu usually is manifested as very distinctive eyes, characterised by their enlarged and featureless white irides (though the anime tends to portray them as a light shade of lavender) with no visible pupils. While active, the pupils become more distinct and the veins near their temples bulge. In the manga and anime, after absorbing Kinshiki Ōtsutsuki's power, Momoshiki Ōtsutsuki's Byakugan takes on a golden colour.

The Byakugan is normally available from birth, however, on rarer occasions the dōjutsu can be awakened. Himawari Uzumaki, a descendant of the Hyūga clan through her mother, generally has blue eyes. When her Byakugan is activated, she gains the normal features of her ancestors' eye. In the novels, it was shown that a Hyūga descendant of a more diluted bloodline may end up only awakening this dōjutsu in a single eye. Also unlike other dōjutsu, transplanted Byakugan can be activated and deactivated at will.

The Byakugan's powers are highly coveted, as evidenced by other villages' attempts to steal it; Kumogakure made various attempts to obtain this dōjutsu. Ao of Kirigakure is the only foreigner known to have obtained a Byakugan from a Hyūga he defeated and went to great lengths to protect it; when Danzō Shimura, a loyal extremist of Konoha, found out about this, he went to similar lengths to retrieve or destroy the eye. In order to reduce the probability of their eyes falling into enemy hands, the main house of the Hyūga place cursed seals onto the foreheads of branch house members which, amongst other things, seals away the Byakugan upon the wearer's death.

Abilities
The Byakugan gives a near 360º diameter field of vision, with one blind spot at the back of the neck above the first thoracic vertebra. It has a powerful range of vision, able to magnify up to cellular level on its targets or view great distances. The distance varies between users and can be improved with training: for example, Hinata Hyūga as a genin could see targets 50 metres away; by age 18, she can see targets 20 kilometres away. Its vision can penetrate through any solid objects or obstructions, and likewise remains unaffected by blinding interferences, though certain barriers may distort the Byakugan's perception to a degree.

It also grants incredible clarity and insight, able to clearly see and analyse all minute details, even at high-speeds, granting a highly accurate sense of prediction to anticipate the flow of events and actions of others. In the anime, the Byakugan is shown able to use infrared to detect a target through their body heat. It can determine the development of one's chakra, even tell if one can mould chakra at all. It can even see the elemental affinity of others. Also, a powerful enough user can see into a target's mind to determine their thoughts and feelings, even look through their memories, which Kaguya could perform to such a level that even Hamura proved incapable of repelling her with his Byakugan. It can also emit powerful chakra pulses to subdue an opponent.

The Byakugan can see chakra to a higher degree than the Sharingan, such as identifying where a person's chakra signature originates from. It can see the very flow of it to track targets and, in the novel, even locate the focus point of an enemy's launched attack to counter and dispel it. It can discern certain types of clones from the real person. Its ability to see chakra is acute enough to see the chakra pathway system and the 361 tenketsu that run along it. The Hyūga have devised a fighting style known as the Gentle Fist to take advantage of this ability, wherein they strike an opponent's tenketsu to either seal or forcibly open them, thus giving the user complete control over their opponent's chakra.

The Byakugan can also decipher whether or not genjutsu is being used on either the wielder or others. However, despite its resistance and penetrative gaze to most targets, certain kekkei genkai can produce powerful enough genjutsu to overpower a Byakugan. According to Hagoromo, the Byakugan can extend the range of genjutsu; Kaguya indeed used her Byakugan in tandem with the Rinne Sharingan to cast the Infinite Tsukuyomi on nations. In the manga, Momoshiki could use his Byakugan to read the fate of other people, though, as he lamented, it didn't allow him to see his own fate.

Prolonged use of the Byakugan causes severe but temporary eye-strain, leaving wielders unable to properly perceive targets. In the anime, it was shown that once manifested, the Byakugan will automatically activate if the user is stressed enough from confrontation even without proper control of it.

Evolution
When the Byakugan of a Hyūga clan member is combined with the chakra of an Ōtsutsuki clan member descended from Hamura Ōtsutsuki, over a certain period of time it evolves into the Tenseigan. When Toneri Ōtsutsuki gains the Tenseigan by taking the eyes of Hanabi Hyūga, he can access the Tenseigan Chakra Mode, granting him Truth-Seeking Balls and physical enhancements similar to the Nine-Tails Chakra Mode. The Tenseigan also provides the ability to control gravitational forces and other telekinetic-like abilities. The Tenseigan can lose its power and revert to the Byakugan if weakened enough in battle.

In the anime, Urashiki Ōtsutsuki is shown to be able to activate the Rinnegan in the same pair of eyes as his Byakugan, and can switch between the two dōjutsu at will.

Trivia

 * The kanji for can also be read as "shirome" or "hakugan". When the latter two readings are used, "白眼" is used to refer to the sclerae.
 * In the anime, the Byakugan's sight is normally illustrated in an inverted black and white colour scheme, however, instances in the manga show no such changes in their sight.
 * In the anime, Hagoromo Ōtsutsuki's natural eyes appeared identical to the Byakugan, implying to have had this dōjutsu as well.
 * When first introduced, Hinata's children: Himawari and Boruto Uzumaki did not have the characteristic white eyes inherited by all Hyūga descendants. According to Masashi Kishimoto, he intended to give it to them but simply forgot to.
 * Kishimoto later essentially corrected his mistake for Himawari by giving her the Byakugan in the Zai no Sho's special chapter The Day Naruto Became Hokage.
 * Boruto later manifests the Jōgan and only in his right eye.
 * The wielder sometimes use hand seals to activate the Byakugan. This is probably due to limited mastery of the dōjutsu for the user. The used seals are: Horse, Tiger with just index fingers, Boar with nearly straightened fingers, Hare, Rat, Dog, Horse, Dog, Hare, Rat, Boar with nearly straightened fingers, and Snake with the right index finger lifted. Sometimes, only the last seal is used.
 * Kishimoto stated in the third databook that if a Sharingan user and a Byakugan user were to mate, their offspring would have one Byakugan and one Sharingan.
 * In the anime it is alluded that while all Hyūga inherit the Byakugan and constantly show its generic physical traits, they must also go through intense training to manifest the dōjutsu's actual powers and that not all actually accomplish.