Zombie Apocalypse

You wake up to a dark reddish hue, and as you analyze the situation, you conclude that you are in a war zone; planes everywhere, a mothership firing beams at the infected while battling one slightly larger than itself. Suddenly, an infected is about to shoot a laser beam at you, but someone reverses it and the infected is pulverized. A massive ship with the codename "Achilles" helps by eliminating several infected, but a light-infected weakens it, forcing it to return to the sea.
Surrealix: Are you okay, friend?
Astra: Make sure there are no serious injuries.
Then, two brothers emerge from some rubble; one looks excellent compared to the other, who has a prosthetic arm and a damaged mask.
Matt: Achilles can't hold on much longer, it has to retreat. Light is using his awakening and we can't risk losing that mothership.
Roger: Exactly, I agree with the leper.
Both notice your presence. Um... who are you?

Try to survive and stop the infection, you must unite all sides, protect Achilles