Before he met Zabuza, he suffered from a belief that he was unnecessary, and served Zabuza because he wanted to feel useful.
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. 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. Haku was a good-hearted, compliant, and eager shinobi, believing that a person becomes truly strong when they have someone important to protect. He had long black hair, pale skin and large, dark-brown eyes, and a slender frame.
Haku was a 15-year-old boy 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.