Preword: Well, shit.
I came up with this idea while doing my Hale/Meer Chronicles, thinking of having Private Jeanette 'AMF' Vasquez as a squad mate, and implying that an 'incident' happened at LV 246.
So I've inserted both universes together.
As this is a story conglomeration, somethings have changed. Androids are an obvious no-no, and pulse rifles are gone. The Nostromo's story has changed slightly, and I had to alter the time table, as Ripley's 57 year hibernation would mean she pre-dates the Mars Archive discovery, which means that interstellar travel had to be achieve before then. Though I use the term hyperspace as a means of travel, this is not to be confused with Star Wars' hyperspace, which is more of a break of reality as oppose to faster-than-light. In this, hyperspace means pre-Relay FTL flight by means of what I've invented as the Yarik Hyperdrive Core; a matter-anti-matter fusion reaction engine capable of creating a copious amount of energy released into an electromagnetically-conductive current infused with the ship to accelerate it to speeds that can make a ship go sixty light-years an hour. In Mass Effect, Relay travel is pegged at about 1 parsec an hour (or about 3,261.667 light years for you sciencey types).
The Alliance is different, too. The founding of the Mars Archives was done by a Corporation, who immediately went heavy into research and development. While the discovery did lead to the formation of the Systems Alliance, it is now a Corporation-ran oligarchy (a government of the privileged few, usually for corrupt, selfish needs) in which the Alliance Military, along with the protection of humanity and the Systems, is now deeply-vested in Corporate Interests.
The Cast of Aliens is completely faithful save for a few instances. Lt. Gorman (played by William Hope) is the only one missing. Sorry, Bill Hope. I did throw him into another role, though. As for the first names of the Marines, I went with the first name of the actors (thus, PFC Hudson is now PFC Bill Hudson, as he is played by Bill Paxton). If the character had a first name (like Ellen Ripley) then the name stays faithful. A few Mass Effect characters make it on, but for the most part, this is Aliens in a Mass Effect Universe.
As this is AU to two different stories, some things will be original. The Sulaco that the Marines arrived on in the movie somehow is empty of personnel while they're getting eaten. Who the hell leaves a ship unmanned? This is a plot hole I will fix, and other explanations as well, as how Hadley's Hope got completely overrun when Newt's father was the only one who was visibly facehugged during the Special Edition. Newt's survival, too, will be better explained.
I will try to stay faithful to Aliens as I see fit, mostly pertaining to the dialogue and interaction of the Marines themselves. Yes, they will be in Onyx armor, but having Vasquez's Smart Gun painted 'Adios' on the side will be there. All guns are Mass Effect guns, including the Smart Guns. All ships (save the Nostromo) are Mass Effect ships. There will be Omnitools, turrets, and even security mechs. The Tracker will be an Omnitool program. The Flamer is now a Tech Attack known as the 'Incinerator' from an Omnitool using Omnigel from a canister.
2nd Lieutenant Jane Shepard is a soldier, fresh out of OCS, making it approximately 2176 (she is now twenty-two). She is not an N7, the Butcher, the Sole Survivor, or the Star of Terra winner. How many combat drops has she had? Uh… two. Including this one.
And if you need an emphasis for mood, check out James Horner's very wonderful original score to Aliens, which you can listen for free on such internet programs like Spotify. Considering I wrote this to the soundtrack… it works.
So sit back, relax, and remember… in space, no one can hear you scream.