A more developed summary of the "Varuna on Oracle" AU I've talked about here and there. It's also the setting for the frankly insane Luther/Varuna/Casra OT3 idea that still relentlessly haunts my brain, but I don't really get into that part here. :P
Moments before Hariette's empty vessel is sealed away with the Profound Darkness, Luther makes a last, desperate attempt to save his creations from the abyss. In a moment of indecision, Varuna reaches out for his creator and escapes, abandoning his Master and fellow goddess Mitra in the process.
Though Luther despairs at losing Hariette, Varuna's survival helps ease some of his terrible loneliness, and the two become lovers. Luther vows to make Hariette whole by using ARKS to undo the seal and defeat the Profound Darkness.
As the only member of the Photoner trio to escape, Varuna feels extreme survivor's guilt. Branding himself the god of faithlessness as punishment, he devotes himself to Luther and watching over Hariette's soul, now dormant as a Cosmogenic Arm. As Luther's servant, he works behind the scenes, using his immense power to eliminate any threat to Luther's goals, in the sincere belief that Luther will one day restore Hariette to her rightful place in the universe.
But as time passes, and Luther's obsession with Xion deepens, Varuna begins to question Luther's actions. Luther insists that merging with Xion and achieving omniscience is a necessary step in removing the seal and returning Hariette's soul to her body. With Hariette's soul fading away, and little progress made on strengthening ARKS to take on a single Falz--let alone the Profound Darkness--Varuna is forced to consider the unthinkable: turning against his beloved savior in order to save his true master.