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Should Liara be considered the Deuteragonist? She's one of the most plot-central squadmates, yes, but I don't think she qualifies. Garrus and Tali are also very plot central in spite of the fact that they can die before the third game. I'd place her on equal footing with Garrus and Tali, with the Virmire Survivor and Joker just below them.
Now, she definitely is the Deuteragonist during Lair of the Shadow Broker. In fact, one might go so far as to say that Shepard's the Supporting Protagonist at that time, but that's one small section of a single game.
For the Optional Party Member sections for Kaidan and Ashley, it should be mentioned that under certain conditions, they will refuse your requests that they return to the Normandy. Those certain conditions being renegade conversation options. It is in fact possible to be stuck without them even though you want'em.
Is Garrus a Byronic Hero? The second game steers him very close to the title. He's got the charisma, disrespect and disregard for social norms, troubled past, cynicism, and broodiness. Is there a quality I might be missing to solidify it or can he be considered one?
Interesting question. Usually, a Byronic Hero is doing something that is clearly immoral/illegal as well. Arguments of vigilantism in a lawless place like Omega I can see going either way, but Garrus' loyalty quest involves assassinating the person who betrayed his group, which would definitely be considered illegal since it takes place on the Citadel. Then again, he can decide against it in the Paragon outcome.
In my opinion, Garrus is right on the edge of being a full fledged Byronic Hero in Paragon playthroughs, but definitely becomes one in Renegade ones.
As far as morals go, Garrus is an outcast towards both C-Sec and the Turian military due to his Cowboy Cop tendencies and refusal to follow orders if he doesn't like them. He's gone so far as to say that he doesn't think he's a very good Turian because "when a good Turian receives a bad order, he follows it." While his rebellious streak doesn't show with Shepard due to Garrus's respect for Shepard, he does have it, on top of, by default, being a vigilante and in service of a Terrorist organization. Along with that, he is shown to be quite ruthless in combat, especially towards those he has a personal grudge against. In my opinion, he starts off the game as a Byronic Hero, and Paragon Shepard can start to bring him out of it, while Renegade pushes him more firmly into the mold.
That said, should the trope be listed under his character page, and Garrus put on the Byronic Hero page?
If you feel that he should, go ahead and do that. He pretty much fits the bill.
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