Zwei  

Phantom, Reiji Azuma, ツヴァイ

In the story, Zwei was just an average tourist from Japan until he saw an assassination in America and got kidnapped. Despite this, his innate survival skills proved useful for an assassin. Afterward, his memory was erased using a combination of drugs and hypnotherapy. The name "Zwei" is merely a code name to indicate that he's the second experimental assassin created by Scythe Master.