Train Heartnet is known within the secret agency of Chronos as Black Cat, for his slick style, his lightning reflexes, and his cold, ruthless demeanour. Trained since childhood as an expert killer, Train lives a life of solitude, until he comes into contact with Saya, a bounty hunter with a wild sense of humour. Things really start to heat up when he's tasked with assassinating a girl named Eve, who just happens to also be an advanced, bio-engineered human superweapon. Will the infamous Black Cat suffer a crisis of conscience? And will his brief memories of a troubled past piece together into something real?