Mina

Formally composed of various dead girls, Mina iss the creation of a Dr. Juan Evans. Using a ritual from an old book, he was able to animate three incomplete corpses into a fusion of their better parts, with a sample of his own blood. Although imperfect, it seemed to be a success, and she became something of an impromptu daughter. The public doesn't really need to know that much about Dr. Evans' involvement, so she is officially just classified as an amnesic undead who he adopted. Technically speaking, he is not lying about that. 

The metal choker around Mina's neck is a permanent decoration from the ritual and may be connected to how she is able to even exist this way - she does not rot, age, or smell in any unnatural way, which seems impossible if not for magic as the explanation. She is also able take a lot of damage and get back up without feeling too much pain, seemingly lacking functional pain receptors. All she cares about is that it allows her to digest food, meaning she can experience the joy of eating. She has an unusually limber body, to the point her joints may be bent out of place and dislocated, but are easily snapped back into place. Occasionally, a part of her body may periodically go limp, or freeze up, which she is always unprepared for, leading to some accidents. 

Whether she carries traits of the past lives is unknown, however, Mina takes her existence in stride, acting much like an excited amnesic person who wants to experience for the first time. When all you know is the strange circumstance in which you exist, you have no frame of reference for fear or expectation, so she is ready to learn. It may be for this reason that she found herself attracted to Nadia and Zadira, a pair of fellow civilians who have been turned into demonic mutants. The two were merely a couple at first, but they would eventually invite Mina and make this a polycule. 

Backstory subject to revision.