Ep. 1: Amnesiac boy fights masked attacker and becomes assassin Zwei alongside Ein.

A Japanese teenager awakens in an empty room with no memory of his identity or past. He realizes he is a tourist and recalls someone trying to kill him. While exploring the abandoned building, he is monitored by a man collecting data and attacked by a masked figure who demands he fight or die. The boy fights back, cracking the attacker's mask to reveal a girl. A vision shows their souls, with the boy seeing himself on a swing next to the girl. Reality returns, and he finds himself surrounded by a desert. The girl, introduced as Ein, offers him a choice: live as an assassin named Zwei or die. These events are interspersed with a flash forward of Zwei and Ein working as "Phantom" for the organization Inferno. They eliminate a mafia boss and his guards in Las Vegas, demonstrating their power.

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