The Kujata Materia allows the equipped player to perform the Tetra-Diaster summon, which deals Fire, Ice, Earth, and Lightning damage to all enemies. If an enemy is less vulnerable to one or more of those elements, the summon will do less overall damage; if an enemy can absorb one of those elements, the summon will actually restore HP rather than cause damage. It also cannot be used with the Elemental Materia. It is a Level 5 materia.
In earlier releases of Final Fantasy VII, this was mistakenly titled Kjata, but this mis-translation was corrected in later releases.