NIL: The Paradox City

NIL- Mutants who have been hunted and persecuted all across the land of Gaia for all of history. Identified by their black eyes and white hair, they have superhuman strength and healing, accompanied by an urge to kill any humans within their vicinity.
Silk is one of these mutants, and has been kept in captivity for her entire life. When she finally escapes her prison cell she, along with two other Nil, are immediately forced into a magical slave contract by a young Gambling Sorceress named Silica. They are forced to do whatever the girl wishes or lose their lives immediately.
Silk, Gnat, Slice, and Silica set out on a royal mission to find the Celestial Heart, a legendary artifact which is said to have the power to resurrect the goddess of Gaia. They must enter an underground palace called the Paradox City and find the Heart, all while trying not to kill each other.