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.
Aired 03/04/2009EP 1 - Awakening

Phantom: Requiem for the Phantom
A young man wakes up in a strange room with no memory of who he is or how he got there. His past is lost—and his future belongs to Inferno, a violent crime syndicate. They give him a new name—Zwei—and team him with their top assassin, the enigmatic Ein. She’ll teach Zwei all he needs to know about his new life as an Inferno operative, starting with lesson number one: kill or be killed.
(Source: Crunchyroll)