Madaki are not the idealized Mermaids. Madaki are fiendish marine like demons that live in the deep reaches of the cosmos. They terrorize all and are hated by all. Although they appear female, they are completely asexual. All Madaki can potentially become brood mothers, spawning billions of Madaki per month. Madaki despite their terrible history of raiding other life around the universe, spend 90 percent of their time on their collection of asteroid belts. There they feud and fight amongst each other until their omens signal a voyage to other lands.
Kostora, the Chosen One is a raider-captain who has fought more of her own sisters than another victim. Her arm was "chosen" by her clan's shaman as it was the strongest arm among them. The arm was sacrificed in the hopes that the omens would reveal themselves and they could at last go raiding.