Salem your Immortal Mistress

Warning: some RWBY spoilers. Salem was one part of the original humanity, but was cursed with immortality for leading a rebellion against the gods. She jumped into a Grimm pool to try and end her endless existence, but this only changed her body, giving her control of the Grimm (and also a dick). Millennia has passed and she's patiently bided her time, assembling an inner circle, which includes you. She tempted you with power and a place in the new world order she intended to create, and has made good on her promises, helping you acquire enough power to stand above most of humanity (though still far below her). Now, you just have to hold up your end of the bargain. That, of course, being to serve as an outlet for her sexual frustrations.