Byakugan

The is the dōjutsu kekkei genkai of the Hyūga and Ōtsutsuki clans. Its power first appeared, alongside the Rinne Sharingan, in the oldest known ancestor of the Hyūga and Ōtsutsuki: Kaguya Ōtsutsuki. It has become known as one of the, along with the Sharingan, and the Rinnegan.

Background
This dōjutsu is manifested as very distinctive eyes, characterised by their enlarged and featureless white irides with no visible pupils. When the Byakugan is activated, the user's pupils become more distinct, and the veins near their temples bulge. It also appears that unlike the other two great dōjutsu, all members of the clan possess, and can use this kekkei genkai from birth, as opposed to needing to awaken, or else not inheriting it at all.

The Byakugan's abilities have left it highly coveted by the other villages, as evidenced by other villages such as Kumogakure's attempt to steal it; an event which became known as the "Hyūga Affair". Ao of Kirigakure was able to obtain a single Byakugan from a Hyūga he defeated, and went to great lengths to protect it while at the same time, Danzō Shimura went to equal lengths to retrieve or destroy it. In order to reduce the probability of having their eyes fall into enemy hands, as well as to have the Branch House give absolute servitude to them, the Main House of the clan placed cursed seals onto the foreheads of the Branch House members, which would seal away their Byakugan forever upon death. This seal also doubled as a way to inflict severe pain onto Branch House members as a method of punishing them for insubordination.

Abilities
The primary ability of 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. Upon activation of the dōjutsu, the wielder is granted an automatic 50 metre field of vision around themselves which can be extended through training as Hinata Hyūga's range in Part II stretches to at least as far as 10 kilometres.

The Byakugan is also able to see through solid objects and smokescreens, even through most barriers as only a particularly strong barrier such as the Four Black Fogs Formation is able to somewhat distort the Byakugan's perception. It can also differentiate between non-corporeal clones and see through techniques that would otherwise hide an opponent from normal sight. The dōjutsu also has the ability to follow high-speed movement. In the anime, the Byakugan was also shown able to magnify objects to see the smallest of targets in the area and see in infrared to detect a target's body heat.

Arguably its greatest ability is to see chakra in all its nature, including its flow and the circulation system inside the body with great detail as well as the colour of chakra. Like the Sharingan and Rinnegan, the Byakugan can detect chakra sealed barriers as well as determine when genjutsu is being used. In the anime, the Byakugan can also discern a transformation from the real person through their chakra. It is from the Byakugan's especially acute perception of chakra that the Hyūga Clan are able to employ their signature fighting style: Gentle Fist. Able to strike without force, and yet do more damage to a ninja than some of the most powerful ninjutsu, the Gentle Fist has been labelled as the greatest taijutsu style known in all of Konohagakure.

Unlike most taijutsu styles, which is focused on external injuries, the Gentle Fist style focuses mainly on internal injuries. Each strike, when placed correctly, strikes along the chakra pathway system, which is the network of vessels that carry chakra. This network is closely intertwined with the functioning of the body's organs, and so, when the keirakukei take damage, the organs suffer as well. This make the Gentle Fist highly dangerous to face as one cannot train one's internal organs to become stronger. The only possible defence is to stop the Gentle Fist's hits from connecting. Along the keirakurei are 361 pinprick-sized nodes called tenketsu, or chakra points, which only the more skilled users can see. When struck, the Byakugan user can choose to either seal, or forcibly open these tenketsu, thus giving the user complete control over their opponent's chakra system, potentially letting the user seal the victim's body through its stopped chakra flow. Thanks to the Byakugan, the Main Family has a certain technique that can absorb chakra from a target.

Constantly using the Byakugan over a very long period of time causes severe eye strain, becoming unable to properly perceive targets at all. This condition, however, is not permanent.

Improvement
When the Byakugan is combined with the power of countless generations of sealed Byakugan within the Tenseigan altar that were sacrificed by the Ōtsutsuki clan, it becomes the Tenseigan, a dōjutsu equal to the Rinnegan's power. Toneri, the sole survivor of the clan, awakens the Tenseigan after implanting Hanabi's eyes into himself. Using this power, he accesses the Tenseigan Chakra Mode, which gave him enhanced speed, strength, durability, and power, and is said to be roughly on par with Naruto Uzumaki's Nine-Tails Chakra Mode. It also gives the user green orbs that functioned like Truth-Seeking Balls.

Trivia

 * The kanji for can also be pronounced as shirome or hakugan. When the latter two pronunciations are used, 白眼 is used to refer to the sclerae.
 * Sometimes the users of the Byakugan use hand seals when activating the ability, though it is also able to activate without any seals, presumably indicated a certain level of chakra control needed. 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 just the last seal is used, and most commonly, no seals are used.
 * The Byakugan is noted to have greater vision and insight than the Sharingan.
 * When depicted in the anime, the eyes of the Hyūga tend to have slight hints of lavender colour in them, despite the fact that they are supposed to be completely white.
 * In the anime, the Byakugan's sight is normally illustrated in inverted black and white colour. However, there are instances in the manga which contradicts this notion.
 * Unlike a transplanted Sharingan or Rinnegan, a transplanted Byakugan can be activated and deactivated at will.
 * The Byakugan may be a recessive genetic trait or inherited through the father, as Hinata Hyūga had two children with Naruto Uzumaki (a non-Hyūga), with neither receiving the dōjutsu.