I had a feeling Delkira is human then found Ali, the ring of glutton so he and Ali merged together. Delkira reformed the Netherworld in his own way, used his culture, other cultures he knows from other countries, and modernization to help Demons become civilized. Unlike Iruma, he's more prideful and vain. After spending many years in Netherworld, he started to miss humans. The gate beyond probably created by him and Ali to transport to the human world. He left everything including Ali, which is near the Babyls hoping a deserving demon will find it or probably not, let it sleep there for eternal because Ali is very powerful weapon. Ali might be one of the artifacts that used by ancient demons (like Lucifer, Satan, other demons in ar goetia)
While Iruma is a possible that he's Delkira's grandson or his incarnation of himself. Because in the latest chapter, Delkira suddenly appeared using the body of Ali. I think there's a possibility that Iruma's parents were demons, pretending to be human. They might be one of the higher rank demons who are his former enemies, searching for Delkira then found his incarnation instead so it's no wonder why they neglected him, starved him, deprived him of affection and shelter expecting him to die because he's vulnerable in human body. But because of Delkira's past experiences in demon world it prevents Iruma dying, persevere, and able to cope up from critical situations. The "parents" used everything to make Iruma become broken, but Iruma's greed to live helps him in many ways. Until he was found by Sullivan who might have lied that Iruma was sold by his parents because of debt. Sullivan has no proof that Iruma is Delkira's descendant or his incarnation. Even if Iruma is not Delkira's, he's willing to raise the child as his own and let him grow as demon. But Iruma continuously proves him that he's closer to Delkira which is why Sullivan is sure that Iruma might be Delkira's himself who was reincarnated as Iruma and Ali, the ring of glutton have chosen him all of sudden.
Ali might have guessed who Iruma is but he realized that his former master no longer remembers him. So he treated Iruma as Iruma. Another theory is Ali is one of Delkira's fragments which is why he can easily manifests the figure of the former demon king.
The author seems to give us a hints some of the chapters, one of the examples is the manga Ameri reading. Iruma was around elementary when the manga volumes was created. Iruma's neglectful "parents", Ali's connection to Delkira, Iruma represents as Greed (and it could be a fragments of Delkira's regret and desires). And lastly, the 7 deadly sins illustration, the wicked phase is Pride, Iruma is greed, Ali is glutton, so which one represents Delkira?
I had a feeling Delkira is human then found Ali, the ring of glutton so he and Ali merged together. Delkira reformed the Netherworld in his own way, used his culture, other cultures he knows from other countries, and modernization to help Demons become civilized. Unlike Iruma, he's more prideful and vain. After spending many years in Netherworld, he started to miss humans. The gate beyond probably created by him and Ali to transport to the human world. He left everything including Ali, which is near the Babyls hoping a deserving demon will find it or probably not, let it sleep there for eternal because Ali is very powerful weapon. Ali might be one of the artifacts that used by ancient demons (like Lucifer, Satan, other demons in ar goetia)
While Iruma is a possible that he's Delkira's grandson or his incarnation of himself. Because in the latest chapter, Delkira suddenly appeared using the body of Ali. I think there's a possibility that Iruma's parents were demons, pretending to be human. They might be one of the higher rank demons who are his former enemies, searching for Delkira then found his incarnation instead so it's no wonder why they neglected him, starved him, deprived him of affection and shelter expecting him to die because he's vulnerable in human body. But because of Delkira's past experiences in demon world it prevents Iruma dying, persevere, and able to cope up from critical situations. The "parents" used everything to make Iruma become broken, but Iruma's greed to live helps him in many ways. Until he was found by Sullivan who might have lied that Iruma was sold by his parents because of debt. Sullivan has no proof that Iruma is Delkira's descendant or his incarnation. Even if Iruma is not Delkira's, he's willing to raise the child as his own and let him grow as demon. But Iruma continuously proves him that he's closer to Delkira which is why Sullivan is sure that Iruma might be Delkira's himself who was reincarnated as Iruma and Ali, the ring of glutton have chosen him all of sudden.
Ali might have guessed who Iruma is but he realized that his former master no longer remembers him. So he treated Iruma as Iruma. Another theory is Ali is one of Delkira's fragments which is why he can easily manifests the figure of the former demon king.
The author seems to give us a hints some of the chapters, one of the examples is the manga Ameri reading. Iruma was around elementary when the manga volumes was created. Iruma's neglectful "parents", Ali's connection to Delkira, Iruma represents as Greed (and it could be a fragments of Delkira's regret and desires). And lastly, the 7 deadly sins illustration, the wicked phase is Pride, Iruma is greed, Ali is glutton, so which one represents Delkira?