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)