Bahamut resides in an otherworldly realm accessed from within
Insomnia's Crystal, a magical stone the kings are sworn to protect until the coming of the True King. On the cover of the Cosmogony books, Bahamut is depicted giving the Crystal to the Founder King.
Final Fantasy XV: Episode Ardyn – Prologuedepicts that the Oracle already had the power to commune with the gods before the Astrals had delivered their decision on who to crown king:
Ardyn Lucis Caelum, the venerated healer of people, or
Somnus, Ardyn's ambitious but ruthless younger brother. Bahamut appeared to
Lady Aera, the Oracle, from the Crystal. She parlayed the gods' choice to Somnus, who appears to have betrayed her and Ardyn by instead declaring himself as the chosen king. When Ardyn sought confirmation from the Crystal, he was shunned by its light due to having absorbed the Starscourge into his own body to save others and Somnus became the Founder King as he had declared.
In
Episode Ardyn, during Ardyn's attack of Insomnia, Bahamut appears to aid Lucis, calling Ardyn by his true name and demanding him to halt. Ardyn responds by coldly telling him he does not intend to kneel before Bahamut now.
A power greater than even that of the Six, purifying all by the light of the Crystal and the glaives of rulers past. Only at the throne can the Chosen receive it, and only at the cost of a life: his own. The King of Kings shall be granted the power to banish the darkness, but the blood price must be paid. To cast out the usurper and usher in dawn's light will cost the life of the Chosen. Many sacrificed all for the King, so must the King sacrifice himself for all. Now enter into reflection that the Light of Providence shine within.
—Bahamut to Noctis
