Hei (黒（ヘイ） , pinyin: Hēi, lit. Black), also known as the Black Reaper (黒の死神 Kuro no Shinigami) or BK-201, is a human who gained Contractor powers. He has worked with various organizations including the Syndicate and CIA. He is the older brother of Bai.
Hei is a young man of slender build with black hair and dark blue eyes. When in his Li Shengshun persona, he wears the casual attire of an exchange student. When operating as a Contractor, Hei dons a bullet-proof trench coat and a white pierrot-inspired mask that fully conceals his face.
After the events that transpire at Hell's Gate, Hei lets his hair grow out and neglects shaving. His trenchcoat has become worn and he mostly wears a ski jacket.
Shortly after learning that Yin is still alive and in danger, Hei cuts his hair back to normal length, shaves, and returns to his "Black Reaper" attire.
As a member of the Syndicate, Hei regularly takes on false identities and personas for his missions and day to day life, such as Li Shengshun (李生舜 (リ・シェンシュン), Ri Shengshun, pinyin: Lǐ Shēngshùn): a good-natured, timid Chinese exchange student who tries to help others but otherwise generally keeps to himself.
Hei is a calculating assassin. Unusually for a Contractor, Hei exhibits and sometimes acts upon emotions. Hei also has a huge appetite, often surprising people with the amount he can eat. Despite having the power of a Contractor, Hei still has his human emotions. He deeply cares for his sister, Bai, and searches for her after her disappearance.
After Yin's disappearance, a drastic change came upon Hei's personality. He takes up drinking, becomes more ruthless, gets angry easily and would often lash out at Suou, slapping her across the face whenever she said something that angered him. He rarely showed such behavior prior to this, but after learning of Yin's whereabouts, Hei reverts back to his previous attitude showing his care for Yin, while also developing feelings of care toward Suou.