Taking aside the Uchiha Clan, the Hyuga-clan is the strongest clan of the Leaf. They are known for their very powerful style of hand-to-hand combat and their bloodline limit of the Byakugan. The Hyuga-clan consists of two family's: the main family and the branch family. The branch family is bound to protect the main family with their lives. Someone who is born in the branch family will never be the leader of their clan.
To keep the branch family under control and the secrets of the Hyuga-clan secure, all members of the branch family are given a special cursed seal on their forehead. Because of this seal, a member of the main family can easily kill a member of the branch family with a few simple hand movements. Also, when member of the branch family dies, the seal disappears and so does their advanced bloodline. This is to make sure no one will ever learn the secrets of the Hyuga family bloodline.
The branch family has always had a grudge against the main family. Hinata's father and Neji's father are twins. But just because off the fact that Neji's father was born a few minutes later then Hinata's father, Neji's father will always be in the branch family and Hinata's father will always be in the main family. Neji's father died protecting the main family. Neji believes it's the fault of Hinata's father, and that's the reason for his hate for the main family.
The Hyuga is one of the strongest clans in the Leaf. They have the bloodline limit of the Byakugan and specialize in Hyuga style taijutsu, also known as gentle fist style. This is the strongest taijutsu style of the Hidden Leaf. The technique is based on the chakra they can release from their hands. This in combination with the Byakugan gives the Hyuga a very powerful advanced bloodline.
The byakugan is a bloodline based ability only accessible by members of the Hyuga clan. This is the sharingan's predecessor. The byakugan is also a pupil based ability which allows physical, emotional, and mental insight. In terms of insight the byakugan is the most superior of the two. Anyone can recognize it just by looking in the eyes because the Hyuga clan family members all have white eyes. The byakugan itself translates into 'white eyes.'
The sharingan did evolve from the byakugan but they are two different powers. The byakugan does not possess the ability to mimic techniques. But in spite of that, it is still powerful. Like said before, the byakugan is the most powerful in terms of insight.
The byakugan's fearful and devastating ability is that it can see through almost anything. It contains the ability to see chakra holes and openings. The jyuuken, which is the gentle fist type taijutsu, is incredibly effective when combined with the byakugan. The jyuuken is a taijutsu especially for members of the Hyuga clan to learn. First they activate the byakugan by performing a few hand seals. Then the use it to look through the person physically. This way they can see the chakra circulating through the chakra highway in their opponent's body. Then they attack by using the jyuuken type taijutsu and they make sure that they aim for their opponent's chakra openings. The users of the byakugan basically hit their opponents chakra openings directly and they can either stop the chakra flow or redirect it. This stopping of chakra and redirecting it is done by forcing the byakugan user's own chakra into their opponents chakra openings. The size of t hese holes are extremely minuscule. It is incredible for anyon e to actually hit those holes considering that they are so small and that there are 361 points in the chakra highway. This is in terms of power and physical insight.
The byakugan has the power of mental and emotional insight. It can see what the person feels and is thinking at the moment just by reading their physical and outer gestures. For example, if one of the byakugan users looked into the eyes of their opponent, they could read what they are thinking. By reading what they are doing with their hands and other body movements, they can tell what that person wants to do. The insight of the byakugan is amazing and fearful. This is all in terms of it's power in mental and emotional insight.
Another of the byakugan's incredible abilities is that it can see 360 degrees around themselves. This allows them to respond more quickly to oncoming attacks. This also gives the byakugan user's opponent an unusual feeling like that their opponent has eyes on the back of their head. These are the incredible abilities of the byakugan. For all we know, there could be more.