I feel so sorry for Vexen. He, next to Zexion, had a horrible untimely death.
In KH, I loathed Kairi. In CoM, it was Axel becaused he killed Vexen T_T And in KH2 It was Sora and Kairi. Kairi becuase she's just annoying and useless in general and Sora because he doesn't understand the struggle Organization XIII is going through. Plus he barley shows any sort of sympathy towards them when they wither away into the darkness. It's sad, really.