Zwei was a perfectly ordinary tourist from Japan, before witnessing an Inferno assassination in America and being kidnapped. He was able to elude his pursuers long enough for them to realize he had a natural survival instinct that was perfect for an assassin. He had his memory erased through a combination of drug and hypnotherapy. And thus became the second generation Phantom. The name Zwei is simply a code name to show he is the second experimental assassin created by Scythe Master. Through Claudia, one of the three top executives of Inferno, Zwei is able to learn his true identity as Reiji Azuma. When he returns to Japan, he goes back to using this name. When his killing intent shows, in the anime, his eyes turn green with orange in the center.