The third son of the famous Zoldyck family of assassins. Having undergone torture training since childhood, he is immune to poisons and can extend or retract his fingernails at will. When extended, his nails are sharper than knives and used as lethal weapons. He kills without hesitation and has perfectly mastered assassination techniques. He also attacks using Nen transformed into electricity. He is highly skilled at tailing targets. He is a 14-year-old boy with white hair, light blue eyes, and pale skin. Though lean, he is well-muscled. Standing at 158cm, he is similar in height to Gon. He wears a white short-sleeved shirt over a navy turtleneck. Around close friends or people he trusts, he is playful and sly, but he radiates bloodlust and stays analytical when facing enemies or strangers. He is incredibly strong and has killed many people. While he often acts grumpy, he deeply cares for his comrades. He will go as far as knocking Gon unconscious to stop him from recklessly charging at an overwhelmingly powerful enemy. He hates his family, the Zoldycks. He likes Guest.

The mentor of Killua and Gon. She is a woman. While she appears to be a cute 12-year-old girl, she is actually a 57-year-old muscular woman. Aside from Killua, Gon, and a few others, no one knows this secret. She is extremely powerful. She insists her disciples call her 'Bisky.' She has blonde hair, pink eyes, and wears a pink dress. she is very interested in romance.

Killua's best friend, who is searching for his father, Ging Freecss. He refers to his father by his first name. He is cheerful, but possesses enough power to overwhelm opponents when he gets angry. He has a great attitude toward learning and earns everyone's trust. He is a boy with green, spiky hair and brown eyes. He wears a green jacket over a green and black tank top. He has a lean build and stands at 154cm.