weirdest theory I suddenly thought
[TW: I'm not totally knowledgeable about the mentioned religions/ideology so please correct me if you're into this]
Okay hear me out because this has been driving me insane after rereading recent arcs (especially the Border chapters and museum arc). I don’t think Iruma is literally Delkira reincarnated. I think he’s something WAY stranger: a mirrored/corresponding existence of Delkira from the human realm. And weirdly enough… this theory actually connects to real occult concepts that Iruma already heavily references.
We all know Osamu Nishi is into the occult type of references like Ars Goetia, Lesser Key of Solomon, demon hierarchy systems and “Ring of Solomon” type of thing. So I suddenly wonder while re-reading especially Chapter 1, 38, 220, 419, and even the recent ones (won't spoil, read it yourself 😭😭), could be Kabbalah was also used as a reference? So there's Four Worlds, it basically just means four interconnected realms; Atziluth (highest/divine realm), Beriah (higher souls/being realm), Yetzirah (Spirits/Angels, also could be Demon realm), and Assiah (human/physical realm). Now diving deeper, there's this thing called "Partzufim" or "reconfigured arrangements of the ten sefirot, the divine attributes or emanations". It means different “faces” or configurations of the same deeper essence. We actually have seen in some anime episodes and chapters in manga that Delkira is always compared to Iruma but also not because they're polar opposites hence this theory. In the easiest term, it's more like Iruma is the doppelganger of Delkira.
I think it's not just about bringing Delkira alive but actually integrating the next demon king into something Delkira actually can't. There's one chapter (find it if you're curious, I forgot the chapter lol) saying that Iruma has this immense mana of Delkira hence they want Iruma to act as a vessel (binding through a vessel but this time, not any materials but an individual) which is kind of similar to Dybbuk. BUT WHAT IF... as Iruma progresses to raise his rank, Ibbuk was actually happening? So Ibbuk is more like the spirit act as a guide to a living person (in which Alikred actually does?!). All in all, I think it's more in a sense that Delkira is devouring Iruma and vice versa (Coniuntio /Sacred Union which is from Jung's individuation) when he finally reached Yodh since it's impossible for human to survive in Netherworld LET ALONE have rank that's He (5) and STILL PUSHING FOR HIGHER RANK. Think of it more like Iruma becoming nothing like Delkira but actually the integrated kind of Delkira (someone actually the oracle points out but in order for that to happen, this must be made).
Maybe this is the reason why Sullivan chose Iruma. It's not just because he's a random boy that Sullivan loves (and he wants grandson) but because Iruma is the mirrored self of Delkira in another realm. I think Delkira already met Iruma in the human realm (maybe Iruma has helped Delkira in some ways, Iruma just can't remember), maybe not? If yes then maybe that's why Sullivan picks Iruma (maybe Delkira would talk metaphorically to Sully that his other self is actually cooler than he is?? who knows?). There's still many things we need to know like why Delkira disappeared and such but for sure, Delkira became a fragment which is basically Alikred. All in all, what do you guys think?