Now, overall I'm not sure what the author's problem is with non-mixed Space Marine units. Personally I find the Sisters of Battle in WH40K to be very cool. I don't play the tabletop WH40K wargame, but I bought some of the Sisters figures (among others) just because they're cool. I sort of like that they have their own units--and the game world background provides a believable reason for the Sisters to exist as they do and for the Space Marines to exist as they do. Besides, since this is an RPG, a GM can simply make up or adapt rules to make mixed units or even proper all-female Space Marine units if desired.
But then I thought about it a bit more and decided that I'd like to do a different take on the Sisters of Battle--a more anime flavored take. The WH40Kuniverse is a pretty cool setting, but not for the types of games I'd like to run. The in-game human society is far too rigid, sexist, racist, xenophobic, religiously fanatic, etc. to run anything in it other that fairly canon games. So I'd rather re-do the campaign universe to make it a bit more "modern" and make the Sisters of Battle into a new incarnation: the Sisters of the Light. Actually, I didn't really make that name up all by myself (*gasp*), Xandria has a very cool song by that name (http://www.youtube.com/watch?v=tFh77pKfAc4).
I started with the basics:
- deadly in combat
- state of the art equipment
- spiritual ethos
Then I added:
- spiritual powers (a la The Force, or qi, or whatever)
- gunships and fast starships
Then sprinkled on some "girly" bits:
- every sister is a Princess of the Order
- every sister has a cool pet (if she wants)
- every sister has a "pony" (horse, chocobo, etc.)
- there are robots to take care of most mundane chores
So, the sisters recruit a bit like the Jedi in Star Wars. Some girls (and only girls, of course) are born with the "Light". This "Light" is a bit like the force, but not so combat/telekinesis oriented. Teams are send out to search for candidates. A team always includes a White Witch, one of those strongest in the Light. Candidates and a few close adult female relatives are taken to the main palace-fortress (Schloss Schwestern, maybe) of the Sisters on their secret base planet (planet name pending). There they are shown the life they will live, both as a princess of the order at the palace and in the brutality of combat. Those candidates who accept the invitation and have the support of their accompanying relatives are then tested further for their physical, mental, emotional, creative, and spiritual qualities. If they pass they are taken on as "little sisters", more formally "Maiden Sisters". Years of education and training follow, until finally they graduate and are accepted into one of the Circles within the order as a full Sister Princess.
Currently, I envision the order as having several military branches:
Valkyries (pilots of flying/transforming mecha, per Robotech)
Scouts (combat biker chicks, with big bikes as in Final Fantasy VII: Advent Children)
Troopers (regular battle infantry, like the Sisters of Battle)
Heavy Troopers (heavy battle support teams; called the "Big Sisters")
Ghosts (stealthy sniper-ninjas)
Pilots (crew for the order's gunships and strike cruisers)