Disclaimer: I don't own Naruto.
The caged bird sings with a fearful trill
Of things unknown but longed for still
And his tune is heard on the distant hill for
The caged bird sings of freedom.
—I know why the caged bird sings by Maya Angelou
The Hyuuga clan keeps dozen of songbirds in gilded cages, lining the Main Family's house and some of the inner Branch Family houses. They chirp and sing whenever someone, anyone comes by, providing an effective defense against would-be burglars as the birds vie for the attention of any watcher.
When Neji is five years old, he decides to set one of them free. The little bird, instead of lingering and singing to him once he is free, flies away immediately, and Neji stands, saddened by the bird's abrupt departure, but glad that it is free.
Then Hiashi shows up, and Neji receives a sound slap across the face; Hiashi has deemed the incident too mild to involve the activation of Neji's cursed seal.
Years later, years apart, and without knowledge of the other incidents, Hinata and Hanabi both do the same thing, with similar consequences.
All Hyuuga Branch members dream of freedom. It is the main thing on their minds, every second of every day.
Freedom is slapped in their faces every day. From the presence of outsiders to the Main family, they see it every day, see what they don't have but desperately want, and they pine for it, endlessly, grasping and never quite reaching.
None of them really know what freedom is. They've lived all their lives according to a mandate: they live for the protection of and at the whim of the Main family. Their lives are in the clan head's hands, and the seals at their brows symbols of their bondage.
Neji too has felt these yearnings, has felt them especially keenly. With his feelings of want comes a peculiar sort of pain, for he has more than one reason to want for freedom from his life, a freedom that he has never known.
Neji does not fit into either world. He is a Branch family member who is neither respected nor particularly well-liked by most of the members of the Main house, whoever they may be. But because of his close relation to the Main house, Hinata's constant attempts to win his friendship and Hiashi's recent show of favor to him, he is not trusted by the Branch house. The Hyuuga clan is a dangerous world, and anyone whom the Branch house thinks might undermine them is cast to the side. Neji does not fit in anywhere; he balances a tightrope, bordered on both sides by oblivion if he falls.
Like his kin, Neji has never known anything but bondage. Bondage to the Main house, bondage to tradition and what's expected of him, bondage to the expectations a Hyuuga must live up to, bondage to world's view of the Hyuuga clan, and he's never known anything else. But instinctively, Neji knows what freedom is, and who has it.
His friends are free. Lee and Tenten and Naruto and the others are free, despite what other problems shadow their lives. They don't wear chains like Neji does; they can shake off their leather bonds at any time and forget. The only one who is trapped like Neji is Uchiha Sasuke, and Neji would not pay to swap his lot with the Uchiha prodigy's; Sasuke's metal bonds are weighted down in blood.
Neji does not know the taste of freedom. But he has seen it on the faces of others enough to want it badly. And there is the cruelest part.
No one in the Hyuuga clan will ever be free. There is too much dragging at them, tearing off pieces of their soul until the greater part is out of their hands and into the hands of others. Freedom is a destination at the end of a labyrinth, and a Hyuuga must slay the Minotaur before they can have it. The problem is, once they have done that, they have no thread to find their way out.
Few ever escape it, and Neji debates whether theirs is a happier lot.
Freedom, Neji knows, comes with a high cost.
Three days after he lets loose the songbird from its cage, Neji finds it on the path in the garden. It is dead. A flash of the Byakugan reveals that it has starved to death.