From what I remember, first shirts can lose the diamond at the drop of a hat. In our technical training squadron our first shirt gave his keys to an Airman leading a barracks detail to open a closet door and didn’t get them back. Our first shirt bounced out of there the next day like he had a bungee cord around his ankles.
USAF First sergeant in the grades of E-7, E-8, and E-9In the United States Air Force, First Sergeant is not a rank, but a special duty held by the senior enlisted advisor of a military unit who reports directly to the unit commander. This billet is held by individuals of pay grades E-7 through E-9 (Master Sergeant, Senior Master Sergeant and Chief Master Sergeant), and is denoted on the rank insignia by a lozenge (known colloquially as a "diamond"). Often referred to as the "first shirt", or "shirt", the first sergeant is responsible for the morale, welfare, and conduct of all the enlisted members in a squadron and is the chief adviser to the squadron commander concerning the enlisted force. Most units have a master sergeant in this position, while larger units use senior master sergeants and chief master sergeants as first sergeants.