A small theory:
There is an entity in Bleach that may rival the Soul King's power, and it is a woman. This is not something officially stated by Tite Kubo or any confirmed information, just a personal theory.
Of course, Bleach is a Japanese work, so it naturally draws inspiration from Japanese culture and mythology. After doing some research, I found several myths that seem to parallel Bleach's setting to some extent.
Izanagi and Izanami are considered the first gods in Japanese mythology. At that time, the world was described as an endless sea. Here we can already see a possible inspiration reflected in Bleach.
Izanagi decided to create land, and this strongly resembles the Soul King's role in Bleach.
Izanagi then married Izanami, and they had a son named Hinokagutsuchi, the god of fire. Izanami died from severe burns during his birth and descended to the underworld.
Here, I assume that Yhwach plays a role similar to Hinokagutsuchi in the story, though with clear differences between the mythology and Bleach.
Later, Izanagi went to the underworld to bring Izanami back. She warned him not to look at her, but he ignored her warning. When he looked, he saw that her body had become a decaying corpse despite still being alive. Enraged, she sent the monsters of the underworld after him. Izanagi escaped and sealed the underworld behind him.
What I am trying to say is that if Bleach follows this mythology, then each character may symbolically represent a deity. This would imply that there is likely a character playing Izanami’s role, and that something similar happened between her and the Soul King, resulting in her remaining there.
After leaving, Izanagi gave birth to several gods from parts of his body:
Susanoo from his nose
Amaterasu from one eye
Tsukuyomi from the other eye
This mirrors what happened in Bleach when the Soul King was divided by the noble clans.
After that, Izanagi no longer appears in the mythology, while Izanami remains in the underworld.
The purpose of this post is to show how Kubo may have borrowed certain events from mythology. By understanding the source of his inspiration, it may be possible to predict what could happen later in the story.
Perhaps the character representing Izanami will seek revenge in the Hell Arc.
This is only a theory, of course.
What do you think?