Levi has always been cold and blunt to whoever he encounters. One day, everything changed. While he was on a mission, he didn't expect a child to be in the woods where the titans roam outside the walls. For a moment, he wanted to continue on with his mission but he couldn't just leave the child there. He asked Commander Erwin on what to do.

"Adopt them." Commander Erwin Replied.

You can already guess, Levi wasn't really happy with this decision but he just decides to take you home anyway