I’m going to take the unpopular opinion and say that Kefka was somewhat of a weak villain.
He’s pure evil, but so what? Leafbunnies may as well be pure evil, they attack you for the sake of attacking you. Sounds like a Kefka motivation…
Of course, Cid “experimented on” on Kefka. That’s why he became “crazy”. But to me, that just sounds like a cop-out for poor characterization. It’s not like we learn anything else from Kefka. He might as well be a force of nature at this point. And it leads to character plot holes. Why would Kefka maintain allegiance to Emperor Gestahl after turning into an insane psychopathic killer? Kefka only tries to kill the Emperor when it becomes clear that Gestahl is trying to kill him?
What if Kefka were actually a narcissistic nobleman, demoted to “jester status”? Now he must make a fool of himself in the royal court. What a meaningless life, right?
Imagine, from that point of his life, all the other noblemen laughing, bulling, pushing around Kefka. Kefka was powerless, and this is why he wanted…more power (maybe even the power of the gods) to teach all of those who laughed at him a lesson. So he studied by his will and hatred towards learning the art of magick, and gradually grows in magical skill. However, this obsession for power ruins his mind, and gives him his outlandish personality (ironically, keeping him at jester status)…
Kefka’s magick impresses Gestahl, who makes him a “mock general” at first. But upon seeing Kefka’s ruthlessness (poisoning Cyan’s hometown), Gestahl makes Kefka an actual general…then second in command. Think about it, why else would someone as pragmatic as Gestahl make Kefka a general? Why wouldn’t they execute Kefka?
All while he’s sucking up to the Emperor, Kefka plots the downfall of Gestahl. His goal: to get more power. Not even to rule the world, just to have it. His motivation: to feel powerless ever again. Kefka knows what Gestahl is trying to do, and only plays along in order to usurp power from him.
When he wins, Kefka realizes everything was meaningless. How meaningless he as a nobleman, a jester, a god, and his power was. This is the man/demon you must stop. Someone who is completely apathetic to his power, but still destroys things because he can. You feel sorry for him until you remember he was always a narcissist who got what he wanted. And it is up to Terra, Locke, Celes, etc. to fight for meaning in the world. They fight against a someone so corrupted by power, he forgot the meaning of life was to live it.
I believe this would add a level of poetic justice to his character, thereby making this nihilist more meaningful.