Byakugan

The is the dōjutsu kekkei genkai of the Hyūga and Ōtsutsuki clans, inherited from Kaguya Ōtsutsuki. It is regarded as one of the, 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 (although 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 the time of their birth. In rarer occasions, the dōjutsu can be awakened. Himawari Uzumaki, for example, who is a descendant of the 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, evidenced by other villages' attempts to steal it; Kumogakure tried various machinations of obtaining a Byakugan during what was called 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 having their eyes fall into enemy hands, the Main House of the Hyūga place cursed seals onto the foreheads of Branch House members which, among other things, seal away the Byakugan upon their actual death.

Abilities
The Byakugan gives the user a near 360º field of vision, except for one blind spot at the back of the neck above the first thoracic vertebra. The range of this vision varies between users and in fact can be improved with training: in Part I Hinata Hyūga can see targets 50 metres away and by Part II she can see targets 10 kilometres away. Its vision can penetrate through most solid objects and obstructions, though certain barriers may distort the Byakugan's perception somewhat. The Byakugan is also able to more effectively follow high-speed movements to better react to them. In the anime, the Byakugan is shown magnifying in on small targets and seeing infrared to detect a target's body heat.

Arguably, its greatest ability is to see chakra to a greater degree than the Sharingan: it can identify chakra by the specific individuals it originates from, determine when genjutsu is being used, and discern certain types of clone from the real thing. The Byakugan's ability to see chakra is so acute that it can actually 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 that specifically takes advantage of this, wherein they strike an opponent's tenketsu to either seal or forcibly open these tenketsu, thus giving the user complete control over their opponent's chakra.

Prolonged use of the Byakugan causes temporary but severe eye-strain, temporarily leaving wielders unable to properly perceive targets.

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

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 its user the ability to control gravitational forces and telekinetic-like abilities. The Tenseigan can lose its power and revert to the Byakugan when 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 inverted black and white colour, however, instances in the manga show no such changes in their sight.
 * Boruto and Himawari Uzumaki, despite being children of Hinata Hyūga, do not have the characteristic white eyes inherited by Hyūga descendants. According to Masashi Kishimoto, he simply forgot to give it to them.
 * 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.
 * 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 Naruto Shippūden the Movie, the Byakugan is able to see the elemental affinity of others.