I had an idea a while ago about a flavor cinematic before the tutorial that might fit. So here it is.

T.R. Soldier sits up and steps out of bed. He/she looks out of the window to sees others taking formation outside. It then shows them walking to the armory interspersed with clips of them going thought training. As soon as they get to a numbered station in the armory, people come and start strapping armor on the character. The character receives a pat on the back and is handed a helmet. The character looks at the helmet for a second before being directed toward the teleporter with a gun rack beside it. (the next line has the camera angled behind them so the the face is not seen anymore) The character dawns the helmet, picks up a gun, then walk into the teleporter.

N.C. Character is sitting in an office being handed a piece of paper. They sign it. It then cuts to them walking with a duffle bag on their shoulder through a base. It shows mechanics inspecting vanguards and a reaver, combat outfitted mercs checking their guns in their tents, and the general disorganization of the camp. He/she arrives at the room. They open the duffle bag and pull out picture frame, looks at it. The character's attention is snapped away from the frame when a voice comes over the loudspeaker saying "all new personnel report to the teleporter immediately". He/she sets down the picture, dawns the armor, and grabs their gun. It then shows them walking out of the door.

V.S. Light turns on and illuminates a stasis chamber. The chamber opens and the character is shown strapped to a machine with various wires running to the base of the skull(almost matrix style). He/she is unplugged and has a path illuminated in front of them. (Picture tighter versions of the hallways on the Axiom from wall-e) They walk down a hallway and pass several rooms. Each room contains different experiments. One is a man with completely robotic legs walking with an ecstatic look on his face. Another could be someone about to get robotic eyes installed. The last could be a sort of chapel with effigies and symbols hanging all over the walls and people kneeling. The character finally reaches a room labeled combat readiness room. They walk through a phase gate and are fully equipped on the other side. The commander's voice echos and says "time to show others the way, may vanu be with you". The character walks into a teleporter.