Major characters that are halfling of some alien, supernatural or "other" race of beings. Espers, Cetra, Lunarians...

Death of a major character (though VIII and IX don't really apply...)

A crystal in some form or other, whether it's of major importance like the crystals in FFI,III,IV,V,IX, and XII or just minor things that don't cross your mind (FFVI,VII,VIII, and X)

The fact that airships are almost always connected to Cid (only four exceptions I can think of)