Sorry but i never played FFVI. Ryushikaze said that Kefka didn't have controll over all magic, and what i know about the game is that is possible to hurt(and kill) Kefka with magic, and because of this, i thought that existed some magic not related to the Goddesses(i heard that the power of the Espers are not related to their power).
If Kefka have controll over all magic, how the heros could kill him with it?!