Phantom: Requiem for the Phantom - Season 1 - Eps 1: Awakening
A teenage Japanese boy wakes up to find himself alone in an empty room with no memory of his own identity or past. He surveys the room he is in and discovers he is a Japanese tourist and suddenly realizes the only thing he can remember is that someone was trying to kill him. While he explores the seemingly abandoned building, he is suddenly attacked again by the masked person from his memories and is told to fight with everything he has or die. Meanwhile, someone is remotely watching his actions. Deciding that he wants to live, he fights back and momentarily gains an advantage; as he attempts to make a killing blow, the mask cracks and his attacker is revealed to be a girl. Instead, he attempts to leave but finds himself surrounded by a desert and the girl, no longer attacking him and introduced as Ein, tells him he will now either live on as an assassin named Zwei or be killed. These scenes are interspersed with a flash forward of Zwei and Ein working together as "Phantom" on an assassination mission. Ein, poses as a maid, along with Zwei, manage to eliminate an entire household of armed guards and the head of a mafia boss in Las Vegas, once again proving their absolute power and indispensability to a mysterious organization called Inferno.
About Phantom: Requiem for the Phantom

Title: Phantom: Requiem for the Phantom
First Air Date: 2009-04-02
Last Air Date: 2009-09-24
Status: Ended
Rating: 7.2/10 (from 31 votes)
Language: JA
Seasons: 2
Total Episodes: 26
Network: TV Tokyo
Genres: Animation, Action & Adventure
Production Companies: BeeTrain
Synopsis
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.
Cast

Miyu Irino
Zwei (voice)

Ayahi Takagaki
Ein (voice)

Miyuki Sawashiro
Cal (voice)

Aya Hisakawa
(voice)

Isshin Chiba
(voice)

Akeno Watanabe
(voice)

Tomoyuki Shimura
(voice)

Ami Koshimizu
(voice)