Kalluto Zaoldyeck is the youngest child of the Zoldyck family, the infamous household of assassins from the Hunter x Hunter series. Born on Kukuroo Mountain, Kalluto was trained in the art of killing from a very young age, just like his older brothers. He is the younger brother of Illumi, Milluki, Killua, and Alluka. A subject of some confusion for viewers, Kalluto is male, a fact confirmed by official guidebooks and hinted at through his use of the masculine personal pronoun "boku" in the Japanese dialogue. His feminine appearance is largely due to his traditional kimono attire, which is a distinctive part of his character design.

Kalluto is characterized by a quiet, obedient, and reserved demeanor. He is often seen silently following orders, particularly from his mother, Kikyo, with whom he shares a close bond. Despite his calm and controlled exterior, Kalluto possesses a notably cruel and brutal side. He has admitted to having a bad habit of toying with his prey during a fight, dragging out the suffering of his victims rather than dispatching them quickly. Beneath his confidence lies a habit of self-doubt; he frequently questions his own skills, especially when comparing himself to the more powerful members of the Phantom Troupe. However, this is balanced by a deep well of inner resilience and patience. He is accustomed to waiting and enduring hardship, a trait that fuels his determination to never give up on his ultimate personal goal.

Kalluto's primary motivation is deeply tied to his family, specifically his older brother Killua. He joined the Phantom Troupe, a notorious gang of Class-A brawlers and thieves, for the express purpose of retrieving his brother and bringing him back home. He replaced Hisoka as the Troupe’s Member Number 4, a position he took over despite being far less experienced than most of the other members. Furthermore, it has been stated that Kalluto feels a sense of envy toward his sibling Alluka, though the specific reasons for this jealousy have not been fully explored.

Within the Phantom Troupe, Kalluto serves as a supporting member rather than a front-line fighter. He joined during the Greed Island arc, where he used his unique abilities to assist the Troupe by tracking down a Nen exorcist who could remove Kurapika's Judgement Chain from their leader, Chrollo Lucilfer. He was also present during the Chimera Ant arc, accompanying the Troupe to Meteor City to eliminate the ant threat led by Zazan. During this mission, he witnessed the overwhelming power of members like Feitan, which solidified his realization that he was vastly inferior to them in strength. Later, he is seen aboard the Black Whale with Illumi, searching for Hisoka as part of the Troupe’s revenge mission.

Kalluto is a Manipulator-type Nen user. His abilities revolve around the use of paper and a paper fan. One of his primary techniques is Dance of the Serpent's Bite (also known as Snake Bite Dance), where he throws sharp paper confetti at a target. Using his fan, reinforced with Nen, he can then lethally cut into the pieces of confetti lodged in the victim's flesh. He also has a technique known as Paper Snow, which gives him versatile control over paper for both attack and defense. Beyond combat, his abilities are highly effective for surveillance and tracking; he can create paper doll lookalikes of people to spy on them and listen to their conversations from a distance. This investigative skill was instrumental in locating the Nen exorcist for the Troupe.