Phantom: Phantom of Inferno - Nitro Archive

A string of assassinations targeting mafia leaders rocks the criminal underworld, giving rise to rumors of a mysterious organization known as Inferno and its deadliest assassin, Phantom.
While on a solo trip to the United States, a teenage boy finds himself face-to-face with this so-called Phantom—only to discover that she's a girl roughly his own age.
Stripped of his memories, the boy is taken in by Phantom and trained in the art of killing. As he learns, he grows into an assassin capable of standing alongside her, and is gradually drawn into the organization's conspiracies.
In this ruthless, lawless world, what will become of the two young assassins...?