This is the first fight Satan might have to sweat a little. It's his first deity level fight.
But indeed, the two characters are actually rather similar. Kefka is extremely unstable, while besides being almost as chaotic, Satan still mostly remains calm. He is prone to accidental violence, but his mind is still pretty stable and hard to shake, unless Kefka know where to strike (Akira Fudou). While Kefka was also caluculative and smart, he was always rather easily provoked.
Also as amazing as Kefka was, he was eventually beaten by one esper and bunch of normies. Kefka might have been a God of Magic, but Satan survived (and is considered a threat by) God of Everything.
Also Kefka needed his tower for his city-level ray attacks, while Satan blew of like a quarter of the moon without any items to help.
The fight will be long and flashy, both parties will have a lot of fun, but eventually Satan wins. Wins even without needing a rely on their haxiest hax - reality warping.