A long time ago, a small rural town in Japan was visited by a man who called himself the Hollow God. Despite his ragged appearance not befitting the stature his moniker would imply, the townsfolk honored his request for food and shelter for as long as he needed it, even going so far as to have a feast in honor of their new guest. Although he initially claimed that he would not be able to repay them, the Hollow God eventually relented to return the kindness that had been shown to him and promised to show his neighbors the truth about himself.
One day, the Hollow God gathered the villagers together and displayed something truly remarkable: by some miraculous power, he had managed to make a toy doll move and dance in front of their very eyes. Some ran back to their homes under the belief that he was some sort of demonic messenger sent from hell, but those who stayed behind in curiosity were shown how this came to be, as the Hollow God explained the use of this source of magic he had dubbed "Existence". He stated that they too could learn to wield this power, and with enough practice, they could further enhance their strength and control over it. The first to experience this "Existence" was a young boy, who soon gained the ability to manipulate the wind around him. Eventually, the others fell in line and requested that the Hollow God grant them similar blessings.
The Hollow God was made a member of the village, where he passed on his knowledge of the medicinal arts to the townsfolk. This had lasted for a little under a week until he stepped outside of his abode one day to take a leisurely walk. When the villagers passed by his residence to give him more food, they found him missing and later unable to be found by search parties. Since then, this mysterious deity had yet to resurface, but the knowledge of "Existence", or EXS, had remained with his students, who swore to preserve them for as long as they and their bloodlines existed.
Whether he had been aware of it or not, the Hollow God's display of EXS had created one of the greatest conflicts in unrecorded human history. Like moths to a flame, those with the ability to manipulate EXS - known as In-Births - had clashed repeatedly in a repeated bid for their own power; factions have risen and fallen as a testament to how important this power has been to them.
This is the tale of In-Births whose natures and rebirths into the world of the Hollow Night have caused their fates to cross in ways none of them would have been able to imagine.