Or it could be about a Mercenary. A member of a mercenary group (think Blue Suns, Eclipse). Not a recruit yet not a leader. And in the intro missions they encounter "something terrible", leader dies his second in command dies too, etc, and player has to take command of their ship at first to save it (field commission as captain in military terms), and then the leadership of the whole Mercenary Group. But not easily, the other members would want this position too so there will be hidden/open struggle for power along with the main plot.
And it all takes place in the far future of course. It would be quite an opposite experience compared to Shepard's. Where Shepard just waltzed thru as Spectre or Alliance Commander, our mercenary will have to improvise as a criminal (according to the laws of several planets), a smuggler, a member of a rival mercenary group, etc