Chapter 1263 The “Hyousube Ichibei” part 2
The moment Kisuke came to this wide cavern and was face to face with Ichibei, he already had a lot of things in his mind. Most notably, Soul King's last words.
He was certain that the Soul King was referring to Ichibei when he said something about 'the being that shouldn't have been born', but Kisuke wasn't so certain as to why the Soul King was making the effort of 'destroying' his work.
With the Soul King's power, there should be no way to have anyone compel him to create the three worlds and start the cycle of life and death by sacrificing himself. In other words, it was the Soul King's idea to create the world as it is. However, why does Ichibei want to protect it? And after all these years, why did the Soul King want to disrupt the balance that he created in the first place?
Of course, from the very start, Kisuke was just speculating all of this because he's not really sure if that's what the Soul King was trying to achieve.
In an attempt to search for clues about it, Kisuke spent most of his time gathering data on Ichigo, Aizen, and Yhwach secretly. It's also one of the reasons why he chose to free the latter two and allow Yhwach to restore his power for a bit. But even if he put so much effort into this, to the point that Kisuke had no choice but to leave the rest of 'migration' in Mayuri's hand, he had almost nothing.
It was then that he finally decided to look at another perspective. The perspective of the 'being that shouldn't have been born'. And to get into that, his first target of investigation was Kazui, the child who accepted Hell.
After that, it didn't take long for Kisuke to piece together the clues that he had gathered when he figured out that Kazui's mission was not to provide safe travel to Hell for the lost souls, but an experiment to increase the Hell's population and further breakdown the boundaries between it and the three worlds.
'If Soul King was the soul of this dead body, then Ichibei is some sort of Spirit that was born from its lingering powers... No... He's probably just a simple maggot or fly that gained sentience after eating and collecting this dead body's flesh. Now it thinks that he's the real thing and trying to 'revive' himself.'
Kisuke intentionally talked in a cryptic way because he wanted the final confirmation from the man himself. Since Ichibei had no more reason to hide anything, he managed to give Kisuke a bit of a straight answer.