From: GuessMyUserName | #041
the Floating Continent actually is a Celes vs Kefka thing
It's more of a Kefka/Gestahl thing than anything else. Totally should've nominated Shadow/Kefka though because that was a lot cooler than the Celes/Kefka thing. And yes, they have a connection, but the game literally does nothing with it other than Celes choosing to cast her lot with the heroes by stabbing Kefka.
Kefka has no rivalry with any specific person in the WoR because you literally don't see him until the end of the game.
And guess who will have a dialogue with him...!
--
"I can set you free, mate."
"My freedom was forfeit long ago!"