[ShadowHeart]

Huge materia is.. huge materia. Really big pieces of materia. You can get 4 of them throughout the game:

* 1 from Corel after saving the town from the train crash (if you manage to do that)
* 1 from Fort Condor when saving the mountain/village from Shinra.
* 1 from the sunken red submarine (if you succeed with the submarine mission)
* 1 from the rocket when you're out in space (if you get the password right before the timer runs up)

Later in the game, you put the Huge materia in Bugenhagen's house, there is one red (used to get Master Summon materias), one yellow (used to get Master Command materias), one green (used to get Master Magic materias) and one blue (used to get the Bahamut ZERO materia).

If you miss one of the Huge materias, doesn't matter which of the 4, there won't be a blue one in Bugenhagen's house, which means you can't get Bahamut ZERO... however, you can dig it up in Bone Village later if you missed it, but I don't know the right spot.