Graviga is a magic spell in Final Fantasy VII Rebirth. It is granted by the
Gravity Materia, and is the strongest gravity spell above 
Gravity and 
Gravira. Gravity inflicts 75% of an enemy's maximum HP as fractional damage.
It is also an enemy ability used against the player by the following enemies: Ironclad, Marquis Valron, and Valron.
Use[]
Gravity can be cast when a fully leveled gravity materia is equipped. The spell deals damage based on the percentage of an enemy's max HP, and is guaranteed to hit. This means the spell's damage is based not on the caster's 
Magic Attack, but on their MP pool and on the enemy's resistance to it, and the 9,999 damage limit (unless broken with the Genji Gloves). Because Graviga is very expensive, it can only be cast by party members with high MP pools.
Very few 
Support Materia can amplify Graviga. Magic Efficiency Materia is perhaps the most crucial, due to its prohibitive MP cost.
Most tough enemies are immune to fractional damage. The player can use Assess to determine vulnerability before potentially wasting MP.