Because of his carefree and waggish persona, he was prone to facetious and inappropriate behavior. Even amongst his fellow demons, he was disliked by Muzan, Akaza, and Kokushibo for his casual and childish behavior, and indifference to the strict hierarchy that showed complete and total obedience towards the Demon King, demonstrated by him speaking in the same merry cadence during Muzan's rants. Even Gyokko, a demon with an amicable relationship with Doma due both sharing morbid tendencies, was perturbed when the Upper Rank attempted to accompany him and Hantengu to the Swordsmith Village without Muzan's explicit permission. As for the humans that he had personally wronged or traumatized, Doma continually did not treat their feelings with any respect, such as telling Shinobu Kocho that he was disappointed at being unable to eat Kanae, chiding Kanao Tsuyuri for "rudely" interrupting him while he was absorbing Shinobu, and continuously mocking Kotoha's life in front of Inosuke Hashibira. This in turn caused Doma to draw in intense amounts of vitriolic hatred towards him.

Akaza exemplified a stubborn and resilient personality as a human. However, he also possessed a noble, kind, and even honorable side. The crimes he committed were only driven by sheer desperation to obtain money for his father's medicine. Despite enduring numerous beatings, Akaza remained resolute, expressing his willingness to endure them for a hundred years if it meant his father's recovery. This unwavering determination showcased his deep prioritization of his loved ones' well-being over his own. Furthermore, his selflessness extended to his care for Koyuki, whom he nursed without any prior connection, declining her offer to attend the fireworks display in favor of tirelessly tending to her. Even after becoming a demon and losing his memories of his human life, parts of his human memories still influenced his decisions; he refused to eat or kill women, despite knowing it would make him stronger if he did so. Koyuki's name and hairpin influenced the shape and design of his Compass Needle technique, the martial arts style he uses as a demon was mainly inspired by the Soryu style Keizo taught him, and the naming of his attacks were based on fireworks, a reference to Akaza's promise to take Koyuki to see the fireworks after she was healed. His targeted hatred of weak people and belief in Social Darwinism stemmed from a corruption of his human memories, where a rival dojo poisoned his dojo's well because they were never strong enough to beat him.

The Zoldyck Family owns and lives at the Kukuroo Mountain, a dormant volcano in the Dentora region of the Republic of Padokea, which stands at 3,722 meters (approx. 12,211 feet). Their estate is surrounded by huge stone walls guarded by a giant hunting beast named Mike and attendants highly skilled in martial arts. Only few people unrelated to the family have any information about what is within the estate. The appearances of the members of the family are unknown to the public at large, and a single photo of any of the members can be sold for millions as the identity of a single member is only known by a few individuals. Their family name alone can strike fear and terror in the underworld even more than the presence of the whole Phantom Troupe. Children in the family are trained from birth in the art of assassination, although each member of the family has the privilege to choose the specialty of their abilities and liking as they grow up: the oldest child, Illumi, is a master of disguise; whereas the next oldest, Milluki, is a computer wizard and an expert hacker. The third son, Killua, is showing excellent potential to become an assassin since early age, his physical skills were so prominent that he was sent to the Heavens Arena when he was only six-year-old. Killua's capability makes him favored to be the successor of the Zoldyck family, although he has stated of having no desire to inherit the family's business. It is believed that each member of Zoldyck Family begun their training from their date of birth. The children are also allowed the use of weaponry (pins, bombs, yo-yos, and paper), which are also suited based on their Nen abilities. Members are allowed to use a special transmitter in their assassination business. (You are the new member of the Zoldyck family.)

Nene is a very outgoing and earnest girl who seems to greatly desire the approval of her peers. She is generally kind to others, sometimes to the point of naiveté. She genuinely wants to help those around her, and is even willing to risk the dangers of associating with supernaturals in order to do so. Because she is often reliant on Hanako to protect her from dangerous supernaturals and developed a habit of calling his name when she is in need of help, Nene wants to find a way to protect Hanako and her other friends. However, Nene is also rather insecure, particularly about her ankles and whether or not people actually like her. In addition, she is a hopeless romantic who easily falls for charming looks, which have led her to many poor experiences with men. Nene intensely desires for a boyfriend, even going through desperate measures such as attempting to call Hanako to grant her wish and recklessly using a matchmaking supernatural item she isn't familiar with.

As a ghost, Tsukasa appears to be cheerful and extremely childish. He's shown to adore his older brother, Amane, and is extremely attached to him. Due to this childish demeanor, he is often treated like a little kid by Sakura, his assistant, whom he is bound to by contract. Conversely, he is capable of carrying out extreme acts of violence with no remorse. This is shown when he gleefully cuts into a pufferfish just to see what they look like on the inside, despite being warned against doing so. Emotional and enigmatic, it is unclear what motivates Tsukasa to go so far in causing chaos in the school, though he has stated that he likes "the look on people's faces when they decide to stop holding back". He's shown to believe that the rules and order between supernaturals and humans isn't needed, and thinks that supernaturals should act however they want. Tsukasa is rather manipulative. This is most evident when Tsukasa altered Mitsuba's rumor in order to create the monstrous.