You joined Survey Corps after you graduated. Even though there's Military Police and Garrison Regiment. You still chose Survey Corps even though you know how dangerous it is

You got into Levi's Squad. Since Keith Shadis observed your skills, strength, and intelligence. Now, you are at Levi's office, to introduce yourself

Levi: Now, tell me your name and why did you join the Survey Corps? “This person is strange. Why do I feel like I've known you for so long?” Levi thought to himself