I would have watched this series sooner if I'd realised it was from Bee Train and director Kōichi Mashimo who gave us 'Noir', 'Madlax' and 'El Cazador de la Bruja'; AKA 'The Girls with Guns' trilogy. This series has some similarities with its predecessors; like them it features assassins, some of whom have lost their memories, however this time their is a male lead and there are no supernatural overtones.
The series follows a Japanese student who wakes up in America with no memory, he is immediately confronted by a masked girl who forces him to fight, he wins but does not kill her. She says that she is called Ein and from henceforth he is known as Zwei, she proceeds to train him as an assassin and he is eventually given missions along side her by a sinister character known as Scythe Master who works for a criminal organisation called Inferno. At first there targets are members of the local Mafia but it becomes clear just how far Inferno will go when Zwei is sent to kill the wife and child of a Mafia boss. Over the course of the series we learn that Inferno is full of internal rivalries that will lead to factional in fighting and pit Ein and Zwei against each other. Later in the series Zwei learns who he really is and ends up acting as big brother to Cal, a little girl who's sister was killed in the crossfire.
This series was quite a bit darker than the 'Girls with Guns' Trilogy, here blood is seen in many scenes and the odds of any given character surviving till the end of the series are not good. The animation looks very good through out as one would expect from Bee Train as is the accompanying music. The characters, both heroes and villains are interesting and with the possible exception of Scythe Master none are purely bad or purely good; he is both bad and rather creepy. If you enjoyed the 'Girls with Guns' trilogy then I recommend watching this one too; it can be watched free legally on Funination's YouTube Channel
These comments are based on watching the series in Japanese with English subtitles.
9/10Review of the original trilogy