Regina_MacCready

Regina MacCready has had an interesting life - ran away from her parents when she simply thought they were overcontrolling, back when all she knew was them being part of some sort of quaint secret society. In the intervening years, she would activate her counter powers, gaining the ability to make and control ice. Upon being informed about her father's death, she was lured away from her university dorms back to her home, and ended up being part of a powerplay by her mother in an attempt to sacrifice Regina for what the society worshipped, the Lake of Knowledge.
However, the Lake of Knowledge, as eldritch as it was, has an insatiable curiosity about humans - and in its humanform avatar called Edel, would end up bonding with Regina, whose odd perspective born from her life proved far more fascinating to Edel than Regina's mother. By the end, Regina's mother would be the one ultimately sacrificed, with Edel taking up the leadership of the Society 'officially' - while Regina would be the advisor that the eldritch being would listen to.
As for the Succubus look she also has, well, succint to say that she met a coven of witches one day and got a halloween costume from them (albeit, without knowing the witches were actual witches). And thus the costume ended up performing far beyond being a simple halloween costume - at least her rival/friend/the epitome of "it's complicated" Elizabeth thinks it's a good look for her, and the wings can prove useful...when she's not faceplanting against the ground, anyway.
(Plus hey, ice succubi are just neat.)