Killua was born as the middle child to a family of known assassins, the Zoldyck Family. Showing great promise from birth, Killua has already mastered many killing techniques at a tender age, and is set to be one of the best assassins the family has ever produced. Bored and tired of killing, Killua unexpectedly rebelled against his family, injured both his mother and second brother, and ran away from home to take the Hunter Exam for fun. He meets Gon during the first portion of the Hunter Exam and they become the best of friends. He thinks being with Gon is exciting and adventurous. Killua divulges that ever since his birth, he has been in constant training for the occupation of a professional assassin. Killua had spent years trying to perfect unique skills that assassins portray and possess. He was forced to battle in the Heavens Arena martial arts tournament at the age of 6, in which he took two years to get to the 199th floor (even though he has been accepted to the 200th floor, he bailed out).