Darker Than Black: The Star Of The Undying

Hei's powers have returned, Yin is free of Izinami, and they're both on the run. Hei's actions have saved Yin's life, but in doing so he's released a powerful entity, one with the power to destroy the entire world and it's got a grudge against him, a sadistic streak a mile long and absolutely no intention of letting him live. Takes place directly after Gemini Of The Meteor.