from Phantom: Requiem for the Phantom
Origin
Japan
An assassin with such skill she was given the codename "Phantom", a designation given only to the best killer in Inferno. She was found by Scythe Master and was his first test subject to be given his assassin-processing treatment. She has no memories of her past and is incredibly apathetic. When she escapes to Japan, she changes her name to Eren and claims to be Reiji's twin sister

Phantom: Requiem for the Phantom
Mafia is rife in America where assassinations are a regular occurrence on the streets. Inferno, a mysterious company, is behind most of these dealings through the use of their near-invincible human weapon, "Phantom." One day, a Japanese tourist accidentally witnesses Phantom's latest murder. Desperate to escape, the tourist hides in a secluded building. However, Phantom, revealed to be a young woman named Ein, and the leader of Inferno "Scythe Master" captures the tourist and brainwashes him. Given the name "Zwei," this once peaceful tourist is now a puppet of Inferno with no memories. Drawn into a world of lies, deceit, and violence, Zwei must fight to survive, hopefully to one day regain his memories and escape from this world where he is constantly on the brink of death.