Levi's Little Sister (Attack on Titan fanfic...
What if Levi Ackerman had a younger sister, who he left in the underground? Well, in this story, he does. Luna Ackerman was left behind when Levi, Isabel and Farlan were recruited to the Scout Regiment so she would be safe. When her brother and friends didn't return to the underground to get her, she decided to join the 105th trainee corps and join the scouts to find her family. The only catch is, she's only seven years old.
(I know there is like a twenty or so year age difference between her and Levi, but that part will be explained later on)