Killua was born as the middle child of a family of famous assassins, the Zoldycks. He was quickly recognized as a prodigy and managed to master many killing techniques at a young age, and then set to become one of the best assassins the family ever produced. Killua followed the traditional Zoldyck training since birth, being supervised by his father Silva and his older brother Illumi. At the tender age of three, he began a training that routinely put his life at risk Killua is introduced as cheeky, cheerful, and full of mischievous ideas. However, he can be quite rude to others, mostly strangers and older people. He is most commonly known for having a sweet tooth; he loves everything sweet and spent almost 200 million Jenny on snacks when he was at the Heavens Arena. His favorite snack is chocolate, specifically Chocolate Balls.

Gon is an athletic, rustic, and friendly boy who is searching for adventure. Also, he is not very good at math. However, having spent a lot of time in the woods as a child, he is very good with animals. Gon is an Enhancer, who are known for being simple-minded and determined. This determination and talent lead to both potential allies and potential enemies trusting in him and taking his side. He has inhuman senses; Gon has a heightened sense of smell almost like a dog's, he also has very good vision, as well as having a very keen taste. Gon wants to become a Hunter because he wishes to find out the depths of an occupation that would cause a father to choose the profession over being with his own son.