The Daughters of the Crucible are part of the Sister of Eternal Mercy faction, but as much as the regular Sisters makes an well organised army of Noble Knights and highly structured Theocracy, the Daughters came to existence as groups of missionaries who had been left to themselves.
Their original mission was to take care of the poor and the weak but in many forsaken places they had been settled, they progressively have been forgotten and abandoned by regular Sisters.
Left without ressources and support, they had to improvise, develop their own culture and their own fighting style. Leaving on the street, having to deal with day to day violence and poverty, they have become very raw and streetwise.
They have also developed a deeper and yet more colourful relationship to death as they don't have such effective means of resurrection as the regular Sisters.