Train Heartnet was Chronos's Number XIII assassin, the Black Cat, until he walked away to live as a sweeper bounty hunter. He partners with Sven Vollfied, a former IBI agent who fights with an attaché case full of weapons and an eye that shows him a few seconds of the future. Their third partner is Eve, a young lab-made girl whose body can reshape itself into blades. The three chase bounties across the country while Chronos keeps an eye on the deserter who once held its top number.