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
Unlike other dōjutsu, the Byakugan seems to be available to its users from the time of their birth and does not need to be awakened through any means. Those who possess the Byakugan have very distinctive eyes: when the Byakugan is not active, they have enlarged and featureless white irides with no visible pupils; when the Byakugan is active, the pupils become more distinct and the veins near their temples bulge. Although the eyes of those with the Byakugan are supposed to be completely white, the anime depicts them with slight hints of lavender.

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 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, leaving wielders unable to properly perceive targets at all.

Improvement
When the Byakugan is combined with the chakra of an Ōtsutsuki clan member, 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.

However, the Tenseigan can lose its power and revert back to the Byakugan when weakened enough in battle, as it did when Toneri was defeated by Naruto.

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.
 * Boruto and Himawari Uzumaki, despite being children of Hinata Hyūga, do not have the Byakugan because Masashi Kishimoto forgot to give it to them.
 * 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.
 * In Naruto SD: Rock Lee no Seishun Full-Power Ninden, whenever Neji is either shock, angered, or serious in situations, his Byakugan is activated.