Quote Originally Posted by Levian
You need to revive aeris first.
But to do that you must get a Multi-Colored Chocobo and fly to an island that isn't in the map. When you get there, walk around counter-clockwise 257 times. You will hear a chime. Fly to another island that isn't on the map, walk around clockwise 257 times. You will get the Jewel Rod. In a fight against a Tonberry, choose the Item option and use the Jewel Rod in the Everyone's Grudge animation (and Everyone's Grudge should do exactly 1337 damage). Aeris will be summoned, and destroy the Tonberry with Holy. After that, Cloud and Aeris kiss and she returns to your team. Simple, huh?

*is squashed by an ice cream truck for being SO idiot*