Killua was born as the middle child of a family of known assassins, the Zoldycks.
He had already mastered many killing techniques at a tender age and was set to be one of the best assassins the family
had ever produced. At the age of three, he started training in tailing that routinely put his life at risk. Sick of killing, at the age of 11 he rebelled against his family, injuring his mother and older brother, and ran away
from home to take the Hunter Exam for fun.
He met his best friend Gon Freeces during the Hunter Exam and they were inseperable for a period of time. They trained and fought several villains on their journey to find Gon's father who is a world renowned Hunter.
This took a considerable amount of time and MANY obstacles. Killua now travels with sibling Alluka Zoldyck