I never really understood why did Sullivan decide to make a human his grandson. He definitely made a lot of moves to push Iruma to become a demon king, but I feel like his motivation for this right now is a bit of a mystery still. We know he misses Delkira a whole lot, so this whole time I viewed this through the lens of Iruma being human somehow being useful for bringing Delkira back. I now realise there might be more to it.
As we are shown in this chapter, all demons, without exception, are subjects to the whims of the Deities. Even the Demon King, despite being a position that allows one to essentially freely reshape the demon society, is someone who can be appointed by a deity without the Three Greats having much say on the matter. It seems like even someone as powerful and crafty as Delkira would have to keep the opinions of the Deities in mind. However, while that is the case when it comes to demons, so far nothing suggests that humans and deities have any connection or relationship.
My theory is that Sullivan's efforts to make Iruma - a human - into a demon king are a lot more politically motivated than we initially thought. This chapter is an example of a deity, which are treated as inherently superior, unilaterally imposing her will on the most powerful in the demon society. If Iruma is not restricted by the same dynamics that apply to demons and deities, him being the Demon King could be a way to upend that order and give the demons more independence from the deities. I also like how this scenario would serve as a neat narrative parallel to Iruma's time with the Many Ears village during his Scala Exam.
