The series follows agent Hei and his comrades in the Syndicate organization, operating in a vastly altered version of contemporary Tokyo to uncover the mysteries of Hell's Gate.

A sequel to the anime series, Darker than Black: Gemini of the Meteor, was broadcast for twelve episodes from October to December 2009.

DVDs of the series included original video animations titled Darker than Black: Gaiden exploring Hei and Yin's relationship between the first and second seasons.

Critical response to Darker than Black was generally positive for its handling of Hei and the other Contractors who fight each other though there was expressure of confusion in regards to the setting and ending.

Ten years ago before the events of the series, a spatial anomaly which became known as "Heaven's Gate" appeared in South America.

Nations and organizations around the world train and use Contractors as spies and assassins, resulting in violent battles for valuable objects and information.

Darker Than Black follows a Chinese Contractor code-named "Hei" as he undertakes espionage and assassination missions in Tokyo directed by the Syndicate.

In his false civilian life, where he is known as shy a student under the alias Li Shenshun, Hei is assisted by Yin, an artificial human known as Doll and Mao, a Contractor trapped in a cat's body and overseen by former police officer Huang.

The series has a villain-of-the-week format, with a variety of characters such as a Japanese Public Security Bureau who oversee the activities of dangerous people with supernatural powers.

[4][5] Since Darker than Black has an original screenplay, Okamura often considered changing the plot, something impossible with manga adaptations, due to the need for consistency with the source material.

[6] Okamura originally wanted the series to be called BK201, a code name, but the anime staff considered it weak and Darker Than Black was suggested by an Mainichi Broadcasting System employee.

[9] The handling of the two Gates prominent in the series' world building was inspired by Roadside Picnic, a novel by Arkady and Boris Strugatsky.

The second half, since this original show needs to be put into an end, it is Shōtarō Suga handling the role as his first time being a series compositor.

Nomura wrote multiple episodes focused on relationships as well as the final parts involving Amber, giving her a tragic ending despite the character staying on Hei's side until her death.

Then Suga, the most important writer in the Darker than Black series, handles high concept and main plot related arcs, with Hei on the spotlight.

And then comes the inside-the-Gate episodes is the first time change really takes place for Hei's character arc after meeting a man who shares the same dreams as him.

Okamura found early designs unacceptable; until his image of the characters matched Iwahara's, the pictures were redrawn many times.

[13] The lyrics of "Howling" focus on Hei's characterization with Okamura commenting that parts of it delve into elements the character briefly saw.

[14] The soundtrack has 20 tracks, including the opening and closing themes performed by Abingdon Boys School and Rie fu.

Some of the background music is typical Kanno as heard in Ghost in the Shell: Stand Alone Complex, but other tracks are livelier; she wanted to write glamorous songs.

[21] The ninth and final set included an additional episode, "Beneath Cherry Blossoms in Full Bloom" (黒の契約者- 桜の花の満開の下, Sakura no Hana no Mankai no Shita),[21] which explored the characters' romantic relationships.

A Blu-ray box set, which included a guidebook and several unreleased musical tracks not available on the original soundtrack, was released in Japan on September 30, 2009.

[52][53] The manga is set one year after the events of season one, and focuses on Hei on a mission to stop one Contractor from giving civilians the chance to become like him.

An Anime News Network reviewer, Theron Martin, wrote that although the setting was unclear, its narrative and cast were appealing.

[71][72] The series' final episodes received mixed reviews; Hei's character arc and his relationship with Amber and Yin were praised, but the ending was considered rushed.

[1] A retrospective Fandom Post reviewer said that the series subverted viewer expectations because it aired in the same time slot as the popular Code Geass with appealing characters and fight scenes.

Fans were disappointed by the ending's lack of resolution, to which character designer Iwahara responded with his manga Dimension W.[76] An AnimeNation reviewer said that the series was less popular in Japan than the West, and the Japanese audience was surprised by a sequel.

[77] The series has been compared to X-Men comics for its handling of supernatural fighters,[78][72][79] and to Cowboy Bebop for Hei's enigmatic characterization and stylishness.

[71] Tomoko Kawakami's performance as Amber, the actress' final work before her death, was called "solid";[72] Jason Liebrecht's Hei was described as "a schizophrenic variation" of Syaoran from Tsubasa: Reservoir Chronicle.

[70] The second opening theme, "Kakusei Heroism" by An Cafe, was praised; "Dreams" by High and Mighty Color was said to lack the appeal of the first ending, "Tsukiaraki".