, also known as , is the protagonist of the 2007 anime Darker than Black by Bones. Codenamed "Hei", he is portrayed as a Contractor, a man with supernatural powers with Hei being able to generate electricity. In Tokyo, Hei works for an organization known as the Syndicate and earns the nickname due to his skills as an assassin. During the series, Hei's backstory of his mission involving his missing sister is developed. Hei also appears in the sequel Darker than Black: Gemini of the Meteor as the mentor of young Contractor Suo Pavlichenko while searching for his partner, Yin. He is also present in the inter-sequel original video animations Darker than Black: Gaiden, which explores his escape from the Syndicate with Yin between the events of both anime.
Hei's character was created by anime director Tensai Okamura, who cited espionage, ninja, and dual-personality influences in contrasting his daily life with his gruesome work. Yuji Iwahara faced multiple difficulties in making his design appealing, while Okamura was surprised by Hei's popularity in the series with male and female viewers. In the anime version, Hei is voiced by Hidenobu Kiuchi in Japanese and Jason Liebrecht in English.
The character appeared in a number of popularity polls about anime characters, and was considered one of the best male characters from Japan during the 2000s. Critical response was mainly positive, noting his dual personality; Hei was initially seen as mysterious at the beginning of the first series but quickly developed into more a caring character. His role in the OVAs and his initial relationship with Yin were praised, but his darker portrayal Gemini of Meteor and his poor relationship with Suo had a mixed response.
Creation
Director Tensai Okamura created Hei. Okamura cited a number of influence for its creation, including the concept of a ninja-type spy working for Tokyo which he saw when he was young. He wanted Hei to appear as a nice, unaffected young man of good character. As the character is portrayed as an assassin who often does not want to kill targets, Okamura wanted the viewers to judge Hei themselves. Okamura wanted Codename BK201 as the series' title, but the anime staff found it too weak and Darker Than Black was chosen by a member of MBS TV. Hei's codename was originally 201-BL as 201 was Okamura's apartment number. As Hei's state of mind remains unknown in early episodes of the series, Okamura said that the lyrics of the anime's theme song,"Howling" by Abingdon Boys School, give multiple hints about how the character thinks.
First-anime writer Kurasumi Sunayama said that Hei is humorous as he pretends to be a Chinese student. Episode twelve raises the possibility that Hei is not a real Contractor because of his sensitivity. Yuuichi Nomura, known for writing tragic storylines, wrote the episodes about Hei's issues with his former Amber who holds romantic feelings for him. Nomura focused on the fact that the two would never be together, and Amber dies in the finale. Main writer Shōtarō Suga wrote the episodes in which Hei befriends a spy who steals an item from the Pandora organization that oversees the supernatural Gates that created the power of Contractors. Hei's friendship with the spy results into a character arc which concludes in the finale; when he has a vision in the Gate of being helped by the dead spy. Hei eventually betrays the Syndicate to protect humans and Contractors as a result after being motivated by the late people he has a vision of. During Gemini of the Meteor, Okamura considered Hei a "rough, working guy", and Suo Pavlichenko took over the lead role to make Darker than Black more innovative.