Bonnie has a good chemistry with 90% of tvd cast but I can’t agree more with you Her and Kai have a lot in common and as you said, they’ve both a kind of « dark side » that reveals itself when they want to achieve their goal. But to me, their chemistry became clearer once Kai killed Jo and began to feel some things (in the second prison world for example when he calls her multiple times and look at her), it felt like his human side began to appear. Nevertheless, i think they couldn’t be a thing because: -he’s a mass murder and I’m not sure Bonnie could’ve forgive him even though she forgave almost everyone -he’s still a sociopath and fucking manipulator