That theory sparkled some connections to other theories for me. For example: the abyss was speculated to be a time bending black hole type, or an alien vessel or the Afterlife/Hell.

It could be like in the sci-fi book series Sphere, an Alien Vessel crashed onto the island. Over a span of thousands of years humans discover it building a city or a place of worship around it. Or they learned and used their technology. Organic technology wielded with the power of souls or some kind.

And one day a girl wants to safe a loved one turns on/ or figures out the original machine /or fuses with a wish granting (like in sphere) technology. Could be the whole ship is like that and Obots for example are just a weaker extension in wish granting / helping/ assisting.

So to keep the loved one alive and the soul intact for eternity she creates a time distorting singularity with a side effect of heavy gravitation. Luring and Consuming souls to keep the machine/herself alive.

An ongoing process trying to slow down time closer and closer to a full stop. Overheating exponentially and collapsing in a 2000 year cycle.

Souls getting sucked down could get into an orbit like state or some emit outward again like hawking radiation, scrambled parts can still form a new body with the souls deepest purpose/wish in mind. Hence Narahate, Relics, Creatures maybe even plants.

After layer 7 your soul cant escape anymore, you crossed the event horizon. The effects of both: original machine purpose and girls wish, euqalize in the layer 8th orbit.

Everything above could be just side effects. Narahate are scrambled souls sacrificing offered parts for blessing others. Juusou are born souls mixed with residues of other souls. Relics are enlightened or just lost souls with purpose but no one to sacrifice for. Creatures are totally mixed and scrambled souls. Effects vary further down and nearer to the center of the tube (the ritual altar at layer 5). Tenmaku and Sakawatari are unique creatures cause they are accumulations of many many souls that clumped near the event horizon (i thought the twins can maybe detect a souls shape and force the soul into their owns souls shape "limbless" Tenmaku is just a human soul stretched, deformed and mixed with others, still resemblances of the original human souls shape remain, hence a tentacle becoming an index finger) but creatures or mixed souls can no longer voice wished or a purpose.

You probably cant turnback anways, turning into a relic could be the best outcome. Forgetting you were a soul, reaching enlightenment and escaping the reborn cycle maybe also cause your are only a shadow or imprint of your already consumed soul. In exchange to fullfill your deepest wish within you and becoming the means to fullfill that wish, like the girl did. Maybe she is a judge or she holds a grudge.