Midnight Magic is a theme set in Japan, Tokyo specifically, in the modern day. It is a setting rife with demons, extra-dimensional invaders, ghosts, wicked mages, and magical girls of light, dark, and neutral varieties. While magical girls may draw their powers from a special lineage, a transformation spell, or something else, the most common (and most powerful) method of empowerment is tied to ancient artifacts that utilize and function with a specific type of magic (what might be termed an 'Element', though many such Elements are unconventional, such as Hope, Love, Time, Law, Holiness, Speed, Illusions, or even 'Rabbits', 'Books', or 'Cosplay', among others). Some artifacts have more than one of these Elements, but the more powers they employ, the more restrictions apply to their wielders and how they conduct their business as magical girls. While many magical girls are good, basing their exploits off of the anime and manga they grew up with, just as many choose to use their power for selfish ends, and 'Dark Magical Girls' use their power for wicked or destructive ends.
The artifacts that empower magical girls and serve as deciding factors in the war against the monsters that prey upon normal folk, however, hold secrets of their own. Each is a living being, and many of them possessed an entirely different form than they do now - and of those, most wish to obtain their true form once more, no matter what they must do, and what magical girls they must use, in pursuit of their mysterious ends.