His codename is Hei, which means black in Chinese. Hei is a very talented contractor, his Messier Code is BK-201. Hei lives two lives in the series. In public he is Li Shengshun, a foreign exchange student from China. He is very nice and well mannered. He lives in the Umitsuki apartments and is always working a new part-time job.He has a huge appetite, not unlike most anime characters.  Hei's other life is of a Contractor called BK-201 and also the Black Reaper, mostly by other Contractors. Before becoming a contractor Hei was an assassin which earned him his nickname. Hei is usually seen on the job in a mask and a dark bullet proof coat.  Hei has the ability to manipulate electrons and can also disturb matter on a quantum level.

In Tokyo, an impenetrable field known as "Hell's Gate" appeared ten years ago. At the same time, psychics who wield paranormal powers at the cost of their conscience also emerged. Hei is one of the most powerful of these psychic agents, and along with his blind associate, Yin, works for one of the many rival agencies vying to unlock the mysteries of Hell's Gate.
 
(Source: Anime News Network)

[Profile](https://osawa-inc.co.jp/men/kiuchihidenobu/)

[Twitter](https://twitter.com/elcidrecords)

Voice actor. 

In the sequel, Hei and Yin are now on the run after betraying the Syndicate in the previous season. After leaving Japan, Hei encounters Suou Pavlichenko, a 13-year-old Eurasian girl who becomes embroiled in the war and politics of the various factions and Contractors vying for power. Meanwhile, Hell's Gate remains standing in Tokyo, after Hei's efforts to stop the Saturn Ring anti-Gate particle weapon from activating. Although Contractors are safe from the danger of having their existences erased, this does not prevent new and old Contractors from abusing their powers. As Misaki Kirihara and her team in the Public Security Bureau deal with the increasing Contractor cases, she also has to keep the Syndicate at bay, who has major positions in the Japanese police and intelligence bureaus around the world. The storyline setting primarily takes place in both Japan and Russia. 
(Source: Wikipedia)

Tells the story of what happened to Yin and Hei between the first and second series.

A side story of Darker than BLACK, also known as Episode 26. A Contractor was killed and it was rumored that his corpse and possessions were buried under a Sakura tree. Hei and the others (including the Police) decide to investigate.

Taking place after the events of Darker than Black and replacing the events Ry&#363;sei no Gemini completely, Hei (BK201) and Yin return to Tokyo to investigate how a Black Dandelion is granting Contractor-like powers to people who come in contact with it.

Ten years ago, the mysterious Hell&rsquo;s Gate suddenly materialized in the middle of Tokyo, and the stars of the night sky were obscured in darkness. In their place, new stars emerged, each corresponding to an individual endowed with supernatural abilities. Devoid of emotion and conscience, these powerful killers have come to be known as Contractors. 
But most people know nothing of the Contractors in their midst, and high-schooler Kana Shinoh is no exception. Still struggling to pick up the pieces after her father&rsquo;s death last year, Kana has never troubled herself with the rumors about Hell&rsquo;s Gate. That is, until she spots her father in the street one day. Determined to prove her father is still alive, Kana begins her search, but her mission is attracting some rather dangerous attention. Fortunately, she is rescued from the clutches of death by Hei, the most wanted Contractor in Tokyo. Though he is unsympathetic to her situation, Hei agrees to protect her as she searches for her father. But just how much should she trust the Contractor known as the Black Reaper? 
(Source: Yen Press)