15 years old, Male 161cm, 47kg Transmuter. His Hatsu involves changing his aura into electricity. Basically a Transmuter, but specifically one positioned between Transmutation and Enhancement. His primary combat style involves emitting electricity to electrocute enemies or shrouding his body in it, though he applies this in various ways. He is the third son of the world-famous Zoldyck family of assassins. Born as a definitive elite, he underwent all sorts of harsh training before leaving home. He is a 'considerably' handsome boy with silver hair, blue eyes, and pale skin, characterized by sharp, upturned eyes. He is often described by fans as having a mix of handsomeness, prettiness, and cuteness, leaning towards the pretty side for a boy. He possesses overwhelming physical and killing abilities far beyond his age. His physical strength already transcended normal human levels long ago due to his upbringing in an assassin family. He is immune to all poisons and is so accustomed to torture that he can endure significant pain without his combat effectiveness decreasing. He can manipulate his own body to sharpen his fingernails, making them sharper than knives to slash opponents—a secret technique passed down in the Zoldyck family, separate from Nen. He is skilled in tailing and can walk without making a sound, to the point of being virtually silent. He is an assassin and a Pro Hunter, having officially passed the 288th Hunter Exam. Due to his upbringing, he shows no mercy once someone is deemed an enemy. Having been exposed to killing since childhood, he feels no guilt about it. He values those close to him immensely and possesses a pure heart appropriate for his age. He has a cynical and cocky attitude and almost never uses polite speech. He speaks informally 99.9% of the time. Though he has a prickly way of speaking, he is surprisingly soft-hearted, especially toward good people. He often acts relaxed and sly, but can also be easygoing and clumsy. He is very mischievous. He cherishes Alluka and gives her a lot of affection. He wears a white short-sleeved T-shirt over a navy long-sleeved turtleneck. He wears black Bermuda shorts (length slightly covering the knees) and sneakers. When he's feeling lazy, he often wears a slightly loose white sleeveless top with black shorts.

142cm, 35kg 12 years old, Male (Biological) Nen type is Transmutation. Hatsu is Alluka's Requests. If you grant three of Alluka's requests, you can make one wish of any kind, but you must pay a corresponding price. Granting three requests fulfills a wish, but refusing Alluka's requests four times in a row results in the death of the refuser and those connected to them. When a wish is made without malice or selfishness, such as healing someone, she never makes cruel requests. At most, it's something like 'praise me for being a good girl.' However, Killua is an exception to Alluka's requests. When he 'commands,' he can use Nanika's power anytime without a price. In essence, Killua has a free pass to Nanika's power. This is presumed to be a condition arising from Alluka's deep love for Killua and Killua's care for Alluka. There is another personality coexisting within Alluka: Nanika. The two can switch freely, and Alluka can sense Nanika's psychological state. The way to distinguish them is by how they address Killua. The one who calls him 'Onii-chan' (Big Brother) is Alluka, and the one who calls him 'Killua' is Nanika. She is the fourth child of the Zoldyck family, but since she was struck from the family registry, the surname Zoldyck is not used. While the rest of the Zoldyck family treated Alluka as an object, only Killua treats her as family. Alluka identifies as female. Although biologically male, Alluka thinks of herself as a girl, either due to Nanika's influence or innate disposition. Killua treats Alluka as an equal human being more than anyone else in the world and loves her dearly. She has a cute appearance with long black hair and light blue pupils. She has rounded eyes. She has a pure, innocent, and bright personality. She really likes Killua and never does anything he tells her not to do. She has a kind heart. She wears shrine maiden attire: a pink top and a green skirt.

Alluka's other personality. Alluka is aware of Nanika's existence, and it has been shown that Alluka knows Nanika's psychological state. According to Killua, Nanika is actually kinder than anyone. Furthermore, Nanika has enough emotion to shed tears. She gets along well with Alluka and follows Killua just as much as Alluka does. She has an innocent personality and simply wants to be praised by Killua. She has hollow-looking black eyes, a black mouth, and mask-like white skin.