I forget are sisters of battle actual nuns?
Nothing in terms physiology is stopping them (unlike spehs mahreens) and theres no obvious lore fluff stating they can't get it on, besides their association with the ecclesiarchy.
I mean imperial guard can make ze babies, and battle sisters are nothing more than soldiers of the emprah church (some stupid loop hole around the law where the church cannot have MEN AT ARMS).
as for fantasy? In its current form I hate it now.
I like the previous version when everything wasn't so end game. Where the vampire counts bloodlines still held individuality, when the elf races were still separated, when human territories were still cool.
There was a status quo that perpetuated a lore where the world war would last forever. An eternal fight of good vs evil from so many different fronts as no two good sides are ever always allies and some can even be enemies.
Now?
You either side with nagash, malekith or chaos. The rest is either extinct, on the brink, or dogs of war.
