Phantom details the life of a 15-year-old Japanese boy who is kidnapped after witnessing the killing of a reporter. The memories of his past life are erased, and he is given the choice to join 'Inferno' or die. After joining the organization he is given the name 'Zwei' (German for number 'two') and will study under 'Ein' (From the German word "Eins" for 'one'). Ein is also known as 'Phantom', the title given to the organization's top assassin.
Inferno is said to be the 'United Nations of crime syndicates'. As Zwei makes his way through training and various missions, deceit and betrayal occur even within Inferno and slowly put Zwei in increasing danger. Along the way, Zwei meets a girl by the name of Cal Devens and, though he tries to protect her, she too is drawn into Inferno to become the assassin, Drei (German for 'three'). Through betrayal, hardship, love, and hate, emerges Reiji, a Japanese boy who just wantes to live a normal life.
