Killua Zoldyck, heir to the infamous Zoldyck assassin dynasty, endured brutal conditioning from birth to hone his lethal talents. His parents, Silva and Kikyo Zoldyck, subjected him to poisons, electric shocks, and physical torture, forging near-superhuman resilience. By three, he practiced stealth through tailing exercises; by six, he battled in the Heavens Arena tournament, reaching the 200th floor within two years. Though deemed the family’s most gifted successor, Killua increasingly questioned this violent legacy. At eleven, he shattered expectations, attacking his mother and brother Milluki before fleeing to take the Hunter Exam. There, his encounter with Gon Freecss sparked a transformative friendship. Killua’s initial detachment and violent impulses gave way to fierce loyalty, prioritizing Gon’s well-being over ingrained assassin instincts. His psyche, however, bore scars from his brother Illumi’s manipulation—a Nen-infused needle implanted in his brain to enforce submission and retreat from formidable foes. During the Chimera Ant arc, Killua ripped out the needle, dismantling Illumi’s control and reclaiming his autonomy. A Transmuter in Nen combat, Killua converts aura into electricity, drawing from childhood torture to forge techniques like Godspeed, which heightens reflexes and speed, and Thunderbolt, a ranged electric strike. Earlier, after injuring his hands in Greed Island, he wielded yoyos as improvised weapons. His assassin training also granted unmatched physical prowess, poison immunity, and tactical ingenuity. Killua’s defiance crystallized in protecting his sister Alluka, host to the enigmatic wish-granting entity Nanika. Defying his family’s exploitation of her powers, he rescued Alluka, using Nanika to heal Gon post-Chimera Ant crisis. This act severed his ties to the Zoldyck legacy, prompting him to prioritize Alluka’s safety over reuniting with Gon. Throughout his journey, Killua evolved from a detached killer to an independent agent. The Election arc saw him confront Illumi directly, asserting his freedom. His story culminates in wandering the world with Alluka, symbolizing his rejection of violence-driven destiny. In non-canon films like *Phantom Rouge* and *The Last Mission*, Killua aids allies against external threats, upholding his role as a strategic fighter and steadfast companion, consistent with his core identity of adaptability and loyalty.