Haku was a young man with an androgynous appearance and was even viewed as being beautiful by Naruto, who exclaimed that he was "prettier than Sakura", even after he informed him that he was male. He had long black hair, pale skin and large, dark-brown eyes, and a slender frame.
Haku was a good-hearted, compliant, and eager shinobi, believing that a person becomes truly strong when they have someone important to protect. Despite his talent for battle, and incredible abilities, Haku disliked needing to kill others in his role as a tool, and avoided doing so whenever possible. When forced to face an opponent, Haku did all that he could to avoid inflicting great harm, even putting them into a death-like state to prevent them from fighting further, as he did to Sasuke during their battle. Before he met Zabuza, he suffered from a belief that he was unnecessary, and served Zabuza because he wanted to feel useful. Because of Haku's pure, kind-hearted personality, Zabuza believed, despite his deeds as his tool, Haku would be able to thrive in heaven while he was condemned to hell.
Due to his androgynous appearance and female voice actresses Haku is often mistaken for a girl.