Byakugan

The is the  dōjutsu    kekkei genkai  of the Hyūga and Ōtsutsuki clans, inherited from Kaguya Ōtsutsuki. 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. Unlike other dōjutsu, the Byakugan is normally available to its users from birth, and 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 characteristic white, featureless eyes of her ancestors.

In the novel adaptation, it was shown that a Hyūga descendant of a more diluted bloodline may end up only awakening this dōjutsu in a single eye.

The Byakugan's abilities have left it highly coveted, as evidenced by other villages' attempts to steal it; Kumogakure used various machinations to obtain a Byakugan during the "Hyūga Affair". Ao of Kirigakure is the only foreign power known to have obtained a Byakugan from a Hyūga he defeated and he goes to great lengths to protect it; when Danzō Shimura, a loyal extremist of Konoha, finds out about this, he goes to similar lengths to retrieve or destroy it. Unlike other dōjutsu, transplanted Byakugan can be activated and deactivated at will. 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, among other things, seals away the Byakugan upon their death.

In the manga, after absorbing Kinshiki Ōtsutsuki's power, Momoshiki Ōtsutsuki's Byakugan takes a gold colour.

Abilities
Once manifested, the Byakugan will automatically activate if the user is stressed enough from confrontation. The Byakugan gives the user a near 360º diameter field of vision, with one blind spot at the back of the neck above the first thoracic vertebra. The range of this vision 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 and obstructions, and likewise remains unaffected by blinding interferences, though certain barriers may distort the Byakugan's perception. The Byakugan is able to follow high-speed movements and analyse their opponent's actions, which allows the user to predict and better react to them. In the anime, the Byakugan is shown magnifying in on small targets and seeing infrared to detect a target through their body heat. In the anime, a powerful enough user can see through one's thoughts and feelings, which Kaguya perform to such a level that even Hamura proved incapable of repelling with his Byakugan. It can also emit powerful chakra pulses to subdue an opponent.

Arguably, its greatest ability is to see chakra, which it can do to a greater degree than the Sharingan: it can identify chakra by the specific individuals it originates from, see through genjutsu plus determine its nature and when it has been used. It can also 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 style of combat 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.

According to Hagoromo, the Byakugan can also be used to extend the range of genjutsu. Kaguya did so in tandem with the Rinne Sharingan to cast the Infinite Tsukuyomi on whole nations.

In the manga, Momoshiki could use his Byakugan to read the fate of other people, though 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.

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 accesses 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.

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.
 * 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 corrected his mistake for Himawari by giving her the Byakugan in the Zai no Sho's special chapter The Day Naruto Became Hokage. While activated, her eyes take on the normal characteristics of the dōjutsu. When not in use, she has her original blue eyes.
 * Boruto later manifests an unspecified dōjutsu and only in his right eye.
 * The Hyūga sometimes use hand seals when activating their Byakugan, though this is not done consistently. The used seals are: Horse, Tiger with lifting 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 straight up. 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, the Byakugan can also determine the development of one's chakra. In episode 198, it was able to see if one has the ability to mold chakra at all. In Naruto Shippūden the Movie, the Byakugan is able to see the elemental affinity of others.
 * Despite its resistance and penetration to most sources of interference, certain dōjutsu can produce powerful enough genjutsu to completely fool a Byakugan.
 * On the cover of chapter 8 of the Boruto series, Momoshiki Ōtsutsuki was show with a distinctly yellow Byakugan.
 * In the anime it is alluded to 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 Hyūga are actually able to accomplish this.