Why is Train Heartnet called Black Cat? The main character of Black Cat, Train Heartnet, is called Black Cat. Where did that name come from? Is it a reference to him being an assassin and, as such, being "bad luck" for people whose paths he crosses?
He called himself Black Cat because he brings misfortune. He also said to his victims I have come to deliver some bad luck before he kills them. 

The motive of the bad luck also is shown in his number (13) and his birthday (13.4.; 13 => number of bad luck in western countries, while the four is the number for bad luck in Japan). Also his name has 13 characters.