Kip. 1: Darker than Black: Kuro no Keiyakusha Gaiden 1

1

After defeating a group of Contractors, Hei and Yin pose as a recently married couple to hide in an inn. As they spend their time, Hei meets a woman who reminds him of Amber. She eventually turns out to be a Contractor who seeks Hei's death. During their fight, Yin intervenes forcing the woman to kill herself. (Source: Wikipedia)