Darker Than Black Omnibus

The celestial bodies of the Tokyo night sky have all disappeared, replaced by strange stars which are linked to Contractors, people who have special powers and lack empathy, enabling them to kill at will. Their amorality makes them targets for organizations who seek to use their power for their own ends, resulting in violent clashes all over the city. The most sought after of these Contractors is the assassin Black, a man whose own partners know little about. Will the law ever catch up to this serial assassin? Enjoy the complete two-volume series in one OMNIBUS edition!

Source: Anime News Network Encyclopedia