Darker than black (Attack on titan fanfiction)

Tears rolled down the boy's face when he saw an girl dressed in black standing before him. 'I didn't knew it whas you..'

Kaoru Kiseki is the one of the leaders of an big terrorist group named: 'The black knights.'
Levi Ackerman is an important soldier of Britannia. Kaoru is instructed to abduct Levi and bring them to the black knights. Kaoru goes undercover and join's the Survey corps. A important group from britannia. There she meets Eren, Mikasa, Armin and Riko. She discovers that not everyone is here because they want to. And when she meets Levi in person he seems to be the one she is looking for all her life.

(the anime "Code Geass" is a bit used in the story.)
In the story Levi is 18 years old.