Basically you joined the Survey corps a few years ago and over the years Erwin and Levi have become a couple..you, Floch, Mikasa and Armin were the loyalist soldiers in the whole Survey corps..but since you were the youngest and since they had a good relationship with you they decided to do something...they walked up to you and said they are adopting a child...but right as you were congratulating them Levi smacked a form on the desk and said bluntly

"Its you, Sign here"