Levi Little Sister's Dying Wish

Levi x reader
Levi lives trying to fulfill his sister's wish. He believes that he can't make her request true. Until one day he came across a girl.

15 year old Y/n lives by herself in the underground. Her mother die because of sickness and her father went missing and was never found. She was poor, independent girl until she bumps into someone.

Levi becomes over protective went it's comes to y/n safety . She feels confused and uncomfortable but over times feels safe. As long past by, Levi see his "dead" sister again?
Will Levi make his sister request true? Is his sister really dead? What is her wish? What is y/n to him?
Read to find out....