Levi is eren's adopted older brother
Levi's mother manages to escape the underground with Levi before dying from her disease.
Levi sits with his mother's corpse in an alley, lots of people walk by but no one helps him.
A pregnant Carla Yeager walks pass an alleyway on her to the doctors when she hears a noise, something inside her tells him to walk in so she does and sees the shocking site of a dead body and a small child.
Being pregnant and thinking if that was her child she would want someone to help so walks further In and bends down in front of the child who is a boy and talks to him In her most soothing voice possible.
She tells the young boy she is going to pick him up and get him some help and to his if she is allowed to touch him.
The boy shakes his head so she asks if he could follow her since he doesn't want to be touched, he nods his head so she gets up and walks away making sure the boy is following.
She takes the boy to her house and makes him a bath and gets the smallest clothes she can find for him.
She then gives him food and water.
Before asking for his name She gets a whispered levi.
She smiles at levi and says hi levi my name is Carla Jaeger ,my husband Grisha Jaeger is a doctor and he should be home soon and if it is okay hw could make sure he is alright.
She asks levi if the woman was his mother and she gets a nod, she comes closer to levi without touching him and says she is so sorry and she wishes his mother had gotten help, but she can't help her now but if it's okay with him she would like to help him, and she offers for Levi to stay with her and her husband.
Levi overwhelmed with emotions cries silently and lunges into Carla's arms.
Grisha gets home and is met with the sight of his wife cuddling a small boy.
He checks on the boy and works out he is about 7 to 8 years old and is malnourished but otherwise healthy.
He tries to convince his wife to send the boy to an orphanage but she stands firm so he agrees.
For the next couple of months levi is fed all he could eat to make him healthy and his and Carla's bond grows deeper He and Grisha get along alright but Clara is his favorite.
He is told be Carla that If he wants he can be a big brother to her baby.
He accepts after feeling the baby kick when he talked, that kick formed an instant connection between the Baby and levi.
Soon Carla gives birth and Levi meets his baby brother Eren Jaeger.
Years go by and eren ans levi are as close as can be, They adore mother/carla and have an good relationship with Grisha.
One day eren and levi go with Grisha to meet a patient, They are met with the patients killed and their daughter Mikasa missing.
Grisha tells them to stay while he gets help but they wander off and come across the missing girl Mikasa and her kidnappers.
Levi and Eren kill the kidnappers ans save Mikasa.