Thinking about the more recent chapters on the manga, I think I've come up with a possible explanation for all the strange happenings centered around the Soul King, Pernida Parnkgjas, and Yhwach. The Soul King is shown to have no limbs, but two of them have been seen, being Mimihagi, his right hand, and Pernida Parnkgjas, his left hand. Pernida, however, is on the side of the Quincies, the people who killed the Spirit King, and Yhwach, the first Quincy, has called the Soul King "father". All of these facts confused me, at first, but I think I may have a theory that explains them.
I remembered when the manga briefly talking about when Yamamoto and Unohana were younger, when the Gotei 13 had just been formed and I thought if maybe it had all started back then. What if the Soul King wasn't always part of Soul Society, or if he wasn't brought under the protection of the Gotei 13 willingly? I think that maybe the Soul King existed when Soul Society from the very beginning, but, at some point in the past, he was subdue, maybe by the Gotei 13 or someone before then, and was dismembered. He was sealed within his palace and his limbs, due to his immense power, came to life as Mimihagi and Pernida. But, why does Yhwach, who claims to be the Spirit King's son, and Pernida, his left hand, want to kill him? I think that the Soul King is actually using Yhwach to try and reform himself. The Soul King wants to become whole again and to be unrestrained as he was before, so he's using his son, Yhwach, to absorb all the essential parts of himself so that he can become whole again. Yhwach has already absorbed the remains of the Soul King's body and Mimihagi. There may be some other parts of him which have yet to be revealed and there is still Pernida who remains unabsorbed, but Pernida is probably on Yhwach's side, knowing that either Yhwach will eventually lead to the Soul King's rebirth or simply because Yhwach is the Soul King's son and Yhwach will eventually betray Pernida and absorb him to reform the Soul King.
What do people think?