Hei
An elite Contractor with the Messier Code BK-201. Hei plays a gentle-hearted student from China named Lee Shenshun when undercover. He becomes an apathetic and guiltless killer when on his missions. Joining an organization of unknown ambitions known only as a Syndicate, Hei is searching for the whereabouts of his sister Pai, whom he lost several years ago when the South American gate imploded. Hei's contract allows him to generate electricity.
Yin
A supporter in Hei's team. She is an emotionless spirit medium known as a "Doll". Very passive and speaking rarely, she is described as having no emotion and incapable of such processes (however as the series progresses she shows a slight human side with hints of emotion). Her primary function is to locate individuals, usually assassination targets, for the team. For this she uses her ability to see anything near water when she is touching water.
Huang
Huang's position can be interpreted as that of field supervisor. He is a human and only possesses strategic abilities. He has a general dislike for contractors and voices it regularly in spite of having to work alongside three of them. Huang passes down orders from the Syndicate to the rest of the team.
Mao
A contractor who has lost his original body and now resides in that of a black cat. He gathers information in Hei's team. His brain is directly connected to the wireless network.