Hei moves through Tokyo like a ghost who remembers being human, and every power he uses costs him something he can't get back. The animation doesn't just show you fights, it shows you a man becoming less of one with each job, each contract, each sacrifice to mystery he'll never fully understand. Yoko Kanno's score wraps around every scene like a question mark that never straightens into an answer, and the show knows that's the point: some gates stay closed, some contractors stay broken, and some stories end before they resolve.

Ten years after a strange barrier known as Hell's Gate appeared in Tokyo, the city has become a battleground for rival organizations eager to learn its secrets. Contractors emerged alongside the Gate: people granted supernatural abilities in exchange for their humanity and conscience. Feared by those who know of them, they are put to use as assassins and weapons by competing agencies. Hei is among the most powerful contractors, known to police only as BK201 and in the underworld as the Black Reaper. Working with his blind associate Yin, he takes on missions for the secretive Syndicate while gradually exposing a sinister scheme that endangers every contractor. Section 4 Chief Misaki Kirihara, meanwhile, finds herself pitted against him. The result is a shadowy blend of action, mystery and science fiction.