One is a nihilistic, broody, and somewhat douchy jackal that that spreads his misery and despair onto others.  

The other is cold, calculative, and ill tempered cat lady who runs one of largest underground criminal empires.  

He always laments the pointlessness of her wealth and power to her eventual demise, yet the bile and vitriol in her heart for others is something he can admire.

She can't stand his constant emo ass slam poetry, but his unending power over darkness and even the undead to some extent can be proven valuable to her own ambitions.  

If I'm gonna have a hero power couple, might as well have a villain one.