In an interview with gaming radio show VGS, Mass Effect lead writer Drew Karpyshyn revealed the original plans for the series.
Karpyshyn had left developer Bioware after writing the first two games in the Mass Effect trilogy, and his planned story was changed by the writing staff who replaced him. In the interview, Karpyshyn detailed what he had planned for the end of the trilogy:
“Dark Energy was something that only organics could access because of various techno-science magic reasons we hadn’t decided on yet. Maybe using this Dark Energy was having a ripple effect on the space-time continuum.
“Maybe the Reapers kept wiping out organic life because organics keep evolving to the state where they would use biotics and dark energy and that caused an entropic effect that would hasten the end of the universe. Being immortal beings, that’s something they wouldn’t want to see.
“Then we thought, let’s take it to the next level. Maybe the Reapers are looking at a way to stop this. Maybe there’s an inevitable descent into the opposite of the Big Bang (the Big Crunch) and the Reapers realise that the only way they can stop it is by using biotics, but since they can’t use biotics they have to keep rebuilding society – as they try and find the perfect group to use biotics for this purpose. The Asari were close but they weren’t quite right, the Protheans were close as well.”
Karpyshyn went on to describe other unused story concepts for the series, including one ending that was scrapped due to its similarity to the twist in Bioware’s previous game, Star Wars: Knights of the Old Republic.