Magical Girl
A long time ago, the feline looking alien species Incubatus Nobilis, commonly known a Incubator, researched ways to counter Entropy, the inevitable heat death of the universe. After many years they came upon the human race and learned that their emotions, which is considered a rare mental defect in Incubator society, hold a great potential. They invented a way to harvest this energy and launched an expedition to the still young planet Earth. Arriving there, they started contracting those humans that held the greatest emotional potential: females on the threshold of maturity.
Incubators offer the fulfillment of a single wish in exchange for a life of combat. The willing girl then has her soul extracted and condensed into an egg shaped gemstone, refrered to as the Soul Gem, it's color and gilding depending on the girls soul. This process expends varying amounts of the Incubators energy, fulfills the wish and grants the girl magic power, turning her into a Magical Girl. The crystallized soul must remain in close proximity of the body to keep it operational as it is in fact more of a puppet, albeit fully functional like any living human. Upon transforming into magical girl form, which includes individual costumes, the Soul Gem takes on a shape that matches the outfit while usually taking on the shape of a ring when untransformed.
Utilizing magic taints the Soul Gem, it must be cleansed to remain operational. This is done by using a Grief Seed that absorbs the black taint. These Grief Seeds are what remains when a Witch is slain, the primary objective Magical Girls followed for hundreds of years. Witches are nightmarish creatures with magical powers whose very existence causes various disasters to happen around them. They hide inside their Witch Barriers, twisted dimensions existing hidden in the human world, spawn familiars to do their bidding and lure humans to their death.
For a long time, it was a well kept secret that witches are in fact Magical Girls whose Soul Gems have been tainted beyond repair by either overusing their magic or falling into despair. The Soul Gem transforms into a Grief Seed and eventually hatches a witch, the original personality replaced by instincts and negative emotions like hate and sadness. Their witch forms and barriers reflect their wishes in dark, twisted forms as if mocking them.
This transformation releases tremendous amounts of energy, which is what the Incubators originally came for. They kept the origin of witches and the Magical Girl's fate secret, justifyed by the fact that humans never asked about it, and harvested the energy without remorse. Some appeared as clichéd animal mascots, others as devils advocates offering faustian contracts, transformed humans into Magical Girls and waited for them to witch out. While these were chaotic and bloody times, the Incubators presence advanced human society much more quickly than otherwisely possible, at least in the alien races eyes.
Not long ago, this system changed. The Ninth Incubator suggested a more organized approach by forming the so called Officio Assassinorum, larger groups of Magical Girls serving under their respective Incubator in a way that considerably increases their life expectancy, thus increasing cost efficiency of creating and keeping them. Their duties and eventual fate are revealed before the contract is made, creating a more transparent working envorinment and a solid base of trust between Incubator and Magical Girl employee. Aside of hunting witches, Magical Girls now also serve as mercenaries to certain human groups, creating a much wider field of expertise.
