Darker than black

There have been rumors of Hell's Gate popping up in Tokyo a decade ago, but high school student Kana is only concerned with her grief over her father's death a year earlier. Then, one day, Kana spots her father on the street and, in her quest to prove that her father is alive, she uncovers the truth of the Hells Gate and the powerful killers known as Contractors who appeared in the city at the same time.