Am I supposed to know who James Vega is?
James just struck me when I started the game with him? Who is he? Where does he come from? Why is he, all of a sudden, in my crew?
Bottom-line: WHO THE HELL IS THIS GUY?
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Vega was tasked with gaurding Shepard while Shepard was in 'prison' on earth. When the reapers attacked he helped Ash/Kaiden get to the Normandy and helped them pick you up. So he is in your crew by pure chance.