Hyuuga's Byakugan

The Byakugan (白眼; Literally meaning "White Eye", Meaning (Viz) "All Seeing White Eye") is the dōjutsu kekkei genkai of the Hyuuga clan.

Background
Those who inherit the blood of this clan have almost featureless, white eyes and 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.

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.[4] Upon activation of the dōjutsu, the wielder is granted an automatic 50 metre field of vision around themselves which can then be extended at their discretion.[5] [6]

The second ability is being able to see through solid objects, as well as telescopic sight. It can also see through most barriers, and other things such as smokescreens,[7] differentiate between non-corporeal clones and see through techniques that would otherwise hide an opponent from normal sight.[8] The distance and the degree of telescopic sight varies from person to person, and can be improved through training. However, the Byakugan cannot see through certain barriers.

The third and one of the greatest uses of the Byakugan is the ability to see chakra, chakra flow, the chakra circulation system inside the body with great detail as well as the colour of chakra.[15] It is from this particular ability that the Hyūga Clan are able to employ their ultimate attack style: Gentle Fist. Unlike the Strong Fist, which is focused on external injuries, the Gentle Fist style focuses 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. There is no defence against the Gentle Fist, since one cannot train one's internal organs to become stronger. The only possible defence is to stop the Gentle Fist's hits from connecting. Like the Sharingan and Rinnegan, the Byakugan's ability to see chakra and its flow allows the user to detect chakra sealed barriers as well as determine when genjutsu is being used.[16] [2] It was shown in the anime that the Byakugan can also discern a transformation, and a real person using the eye's ability to see chakra.[17]

Particularly skilled users of the Byakugan can take the Gentle Fist style one step further. 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. So, with precision, all those points along the victim's body can be sealed, stopping the chakra flow to those areas. 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.

Constantly using the Byakugan over a very long period of time causes severe eye strain, and over using it will make it hard to tell chakra apart even if the user is close to the people. This condition however, is not permanent.