Ein

An assassin with such skill she was given the codename "Phantom," a designation given only to the best killer in Inferno. She was found by Scythe Master and was his first test subject to be given his assassin-processing treatment. She has no memories of her past and is incredibly apathetic.

Her name means "a" in German although it were probably meant to mean "one", which would be "Eins".

(Source: Wikipedia)