I'm digging it. Its always great to see more Serenity action and this story started out with a BANG! in the action department.
I'd like to commend you on the storytelling device you utilized in the first chapter, dropping us right into the middle of chaos and disaster before pulling back to how it all began. You do dialogue very well, none of the characters read like they're saying things out of their norm. I like how the story's progressing and the way you're peeling back the layers on Rem...starting to reveal a real character.
My one and only critical advice would be to re-imagine the very 1st paragraph. It seemd pulled straight from the opening scene of Star Wars, with the little rebel ship on the run from the impossibly large cruiser just above an immense planet, however maybe thats just my lack of imagination.
http://www.youtube.com/watch?v=z33-qOXOWS4|this is what I imagined as I read your wordsI applaud the dedication it must have taken to craft a whole 13 chapters ((I too get sidetracked while finishing stories)) I look forward to reading the next few!