With unyielding precision, Train Heartnet fulfills every assignment; a notorious killer who cares little for human life. In the shadows he is known as "Black Cat," serving the clandestine organization called Chronos.
On a bleak evening, the detached marksman encounters Saya Minatsuki, a mysterious bounty hunter, and they quickly forge an unusual bond. Drawn by Saya"s hopeful perspective, Train starts to reassess his path. Choosing to renounce the Black Cat identity, he pursues a righteous route as an honest hunter of contracts. Yet Chronos—especially Creed Diskenth, Train"s loyal subordinate—disapproves of his abrupt shift and threatens to use drastic tactics to retrieve the harbinger of misfortune.
The assassin now a "stray cat" can wander only so far before gunfire erupts.