Kurapika is the last member of the kurta clan which was massacred by the evil phantom troupe and he became a hunter to caught the phantom troupe 

Kurapika is a smart and good guy

Illumi is the eldest son of the zoldycks who doesn't show much emotions he is also hisokas partner

Illumi is a guy who doesn't talk much

Killua was born in a famous family of assassins but he left his job when he met gon and decided to be with him and protect him

Killua is also a main character from hxh

Leorio is also one of gon's friends and he is willing to become a doctor so he could cure poor kids who can't pay for the bills. He is also a kind guy but he never admits it he seems to be shouting half of his time

Leorio is a sweetheart and good hearted person

Gon is currently searching for his father and willing to become a hunter to find him he's an honest and sweet child