Digging through old hard drive backups, Hironobu Sakaguchi posted development notes about Final Fantasy IX online.
This memo appears to be quite early in the game’s development cycle since Zidane’s thief buddies, Cinna, and Marcus, aren’t named yet. The document details the scene with Vivi and the rat boy explaining that Vivi is "the type to listen to everything his juvenile boss says. He is introversive, quiet, obedient, indecisive, pure in heart and kind."
Sakaguchi also has specific notes for the theater fight like giving players extraordinary magic to use. This is probably the "SFX" command during Zidane and King Leo have access to during the battle.
It’s interesting to see how Final Fantasy IX changed. The early plan mentions the fight with Steiner where Oglops freak him out was supposed to be a movie. It’s playable in the final build. Also, the battle where Vivi, Zidane, and Dagger take on Steiner and two Pluto Knights is different. The original plan was to have Zidane trap Steiner in a pincer attack where he would retort, "Darn it. Attacking from both sides, that’s a coward act!" Instead, the battle is just a regular fight with the SFX command in Final Fantasy IX.