Captured within a prison, thinking that her power would not grow, without realizing how that beast empress had started to influence the very nature of life and death, getting absolute authority over them, and finally creating her own realm as a passage through which souls must pass to reincarnate.
In my old world term, she was simply the queen of Hell.
The afterlife that souls were drawn to upon death, the realm of punishment and torment where the wicked were said to suffer for eternity—all of it which I knew in my past world was the place she ruled.
No one knew how. Sometimes after death the reincarnation circles broke. Given they took it as a mistake in their own capability of resurrecting their souls. But in truth, it was her choice. If she got interested in the soul, then that soul becomes a part of her world.
