Darker than Black: Kuro no Keiyakusha (DARKER THAN BLACK -黒の契約者-, Dākā Zan Burakku -Kuro no Keiyakusha-; lit. "Darker than Black: The Black Contractor") is an anime television series, created, directed and written by Tensai Okamura and animated by Bones. It premiered across Japan from April 5, 2007 on Mainichi Broadcasting System, Tokyo Broadcasting System, and its affiliated broadcast stations, with its satellite television premiere in Japan on Animax in May 2007. The music for the series is composed by Yoko Kanno. The series has also been adapted into two manga series, which are serialized in Monthly Asuka and in Young Gangan. The anime also was awarded Best Original Anime of The Year by GoGoplex, a popular magazine for teens.
A second season titled Darker than Black: Ryūsei no Gemini (DARKER THAN BLACK -流星の双子（ジェミニ）-, Dākā Zan Burakku -Ryūsei no Jemini-; lit. "Darker than Black: Gemini of the Meteor") premiered in Japan on October 8, 2009. This was followed by four OVA episodes, which bridged the gap in the stories of seasons one and two. Titled as "Gaiden", they were broadcast at two-month intervals, premiering on 27 January 2010.
Ten years ago, an inscrutable and abnormal territory known as Hell's Gate appeared in Tokyo, altering the sky and wreaking havoc on the landscape. The heavenly bodies disappeared, replaced by false stars. During this time, people possessing various special abilities emerged, each capable of different supernatural feats - these are known as Contractors. Each fake star has a corresponding Contractor, which reacts to their activities. As such, Contractors are usually identified by their star's Messier catalog number. Kept secret from the masses, these individuals are known to murder in cold blood, smothering unnecessary emotions with logic and rationale. Their incredible abilities, however, are gained at the cost of their humanity - Contractors are thus named because of an involuntary compulsion to "pay the price" each time their power is used, which can range from eating particular foods and completing meaningless tasks, to self-harm and having their bodies change in peculiar ways. Various nations and organizations around the world train and utilize Contractors as spies and assassins, resulting in violent battles for valuable objects and information.