Add Shell, and don't make it stackable with protect.

[Jybril]

Isn't that what Protect is in this game?
Shell in FF series - Increases Magic defense. (There's another small alteration in FF6 but still the same thing.)
Protect in FF series - Generally halves all physical damage dealt to the target.
Protect in XIV - Increases the physical and magic defense of target and all party members nearby target.

They basically merged Shell into Protect.
Actually they made Protect, Proshell.