Phantom -PHANTOM OF INFERNO-

Phantom of Inferno is a story detailing the life of a 15-year-old Japanese boy who is kidnapped after witnessing the killing of a reporter. After being kidnapped his memories of his past life are erased and is given the choice to join Inferno or die. He makes the only choice he can to join and is given the name Zwei and will study under Ein. She is also known as Phantom since this is the title given to the organization's top assassin.

[From Wikipedia]