Mass Effect: Shadow Walker

Sable Shepard is many things: an anomaly, an assassin, a criminal, and a man who is supposed to be dead. It's safe to say that he has a lot of secrets. He once had a promising career alongside his brother, John Shepard, in the Alliance military, but a mission gone wrong changes everything. He pays a terrible price to save his brother's life, one that leaves him so scarred that he choses to 'die' and exist as a ghost.

Then Commander John Shepard comes across an alien artifact when responding to a distress call at a human colony. One thing very quickly leads to another, and suddenly there is a very real, very deadly threat approaching the Milky Way - one that can easily wipe out all known life. And John is the one who must save them all.

Concerned for the terrible burden placed upon his brother, Sable steps out of the shadows. As it turns out, it might have been better for the entire galaxy if he had just stayed dead.