Actually it was a fanfiction! It was actually a really interesting one.. almost weaved into the cannon of the story in the actual videogame. Basically each chapter gives you a blurb, one part in the present, one part in the past, and as the story goes along, the past and present meet up together into the story to make you understand what actually happened to the characters.
And best of all.. there's none of that "obligatory sex" or random mary sues that people throw in. It was a genuinely great story.