Just found an unbelievably clever Mass Effect AU, written by someone who was particularly unimpressed with the random “synthetic and organic life can never exist in peace!!” Catalyst thing.
Several decades pre-game, some horrific plague starts wiping out humanity. It’s contagious enough that it’s killing off the healthcare staff first. So humans hurriedly invent AI health staff - and to help them communicate with patients, the AI staff look and act exactly like humans until you notice they don’t eat or breathe...
AIs do their absolute best to save humanity, but it fails and the plague completely wipes out humans, leaving the robots as the only sapient beings on the planet.
Robots go “wait, what the hell do we do now?”, manage to get rid of the plague “now it’s lost its host,” decide to make more robots and build their own society, and start exploring space, where they find the Mars Archives and successfully convince galactic society that they’re not horrible monsters...
Fic goes along approximately similar lines to the game, but usually makes more logical sense, and the author got annoyed with the third game and went “no, I’m not letting any of the good guys die! None of them!”. Features Paragon Shepard as a first-generation AI who was originally programmed as a search-and-rescue paramedic. I think that’s the best blatantly-non-canon Shepard backstory I’ve seen yet.
(She genuinely doesn’t have a given name. She was programmed without one, and - unlike Chakwas and Traynor, who are just as old - she never bothered naming herself. How’s that for an excuse?)
Kai Leng is genuinely intimidating! Eva Core makes a great OC!
Not really a romance fic, but has some nice Shep/Liara, Garrus/Tali and Joker/EDI content. And the explicit sex scenes have thought through their sci-fi implications - proper use of nerve-stim programs, Liara being briefly startled that Shepard tastes like plastic, one bit where Joker has to physically detach himself from his chair before getting started...
I want to play that game!
https://archiveofourown.org/series/161561