>>3833415
Stealing magic sealing equipment, called "The Goddess Magicite" ended up being the plot device for FF12. It just lacked a train.

In FF7. Aerith and her Mom escaped Shinra by train. Although her mom dies, she passes on her special Materia, which summons "Holy".

"Holy" was tentatively the spell used to break into the vault in Versus 13. The ultimate white magic spell "Holy" also goes by "Erase". As in, erasing something from existence, like Meteor. To cancel as spell or curse, such as the starscourge. Or even extinguish immortal souls from existence.
That was essentially the point of "the holy clavis"; to draw in the souls of the dead.

The souls of the dead are responsible for the power of Trance in FF9.
As well as the body of Sin in FFX. Yuna, like Lunafreya, was once planned to be a healer and draw out Sin's toxin from people along her way, like the Starscourge. FF7 eventually has the "geostigma" in Advent Children and Dirge of Cerberus, which is used to trick the planet into thinking the planet is already dead, and manifest Omega Weapon to ripe the lifestream out.