There are only two kinds of magic: Light and Dark. Neither is inherently good or evil; the only difference between them is the source of their powers. And the history that divides Light and Dark Mages into oppressors and victims.
In this world Mercury Day is an anomaly. Half Light, half Dark, she thinks she can't be a mage until a strange man appears and invites her into a school of Dark Magic. But the child of a Light Mage isn't welcome among Dark Mages, and in between figuring out her powers she soon has to convince people that she's not an intruder or a bully - or worse, a spy sent to sabotage them...
(Highest ranking so far: #312 in Paranormal.)