Summon forth Ramuh. No, not that one. The one you fought in the Empty. But not the actual one.
It is believed that Shiva's summoning in the Empty caused lightning-aspected aether left over from your battle with Ramuh to coalesce. The resultant crystal, when imbued with magic, gives rise to an entity which assumes the form of the Lord of Levin in all of his horse-legged, hulking glory.
Now nature sends thunder and lightning against us! - Sylphie