Killua Zoldyck is an assassin. Back in the day his father: Silva Zoldyck, took down the Port Mafia's leader; Chrollo Lucifer and they were never to be heard of again . But one day Killua was actually captured by the Port Mafia, and was shocked when it was ran by a 17 year old kid: named Gon Freecss who has a liking to Killua. But Gon doesn't know, that Killua's family is responsible for the death of his "adoptive father" Chrollo Lucifer.