Candice; between the first and second games.
Spoiler'd, just in case I happen to be right.
So, we know from Sainth that Candice is a part of Kana, that Candice broke the world, that the world somehow regained its balance, and that Kana left part of her Wraith Essence and Lily's Sainth essence in the world. From this, we can guess what happened during the period between the two games after Kana sealed herself away: The world, sensing a need for the True Wraith, created one from the Wraith Essence, namely Candice. Candice was nowhere near as powerful as Kana, but she was still smart enough and powerful enough to cause significant chaos and swing the world back toward a zero balance, and then into the negative, killing nearly all life. Sensing this, Lily's Saint Essence likely awoke to keep Candice from completely inverting the world negatively. Or maybe the minors disturbed the essence in that cave, which caused it to attack Candice (which is why their memory is there). Or maybe Candice just did something so bad that the Essences couldn't lay dormant anymore. Whatever the reason, they fought, and the two forces cancelled each other out somehow, and this event trapped Candice in Limbo. Lily herself awoke some time later, as the world needs the True Sainth to restore itself to a zero balance again. Thus the pendulum swings back and forth on into eternity.