Personally, I believe he's likely half-demon (whether or not he's related to Derkila in some way or not). This idea stems even more since what we know about Ameri being half-human and having her father's bloodline ability. The magic thing is also what originally drew me into the idea that he might not have been completely human too, because Henri stated that human's aren't able to survive in the netherworld, and I feel like he meant it in more of a sense than what happened with Merize, human anatomy might not actually be able to withstand the magical presence of the netherworld, since they aren't used to being around so much mana, hence one reason why Merize began deteriorating after the birth of Ameri.
But the more recent chapters also are interesting too (outside of the Azazel fam drama), the idea that Iruma possesses Derkila's mana, which is strange considering the ring, devours Sullivan's mana. Sure it could simply be because the ring was somehow created by Derkila, but his massive presence in Iruma's time in the netherworld is strange in and of itself; because Derkila loved Sullivan, so why is he deadset on keeping his presence as Ali a secret from everyone? As well as the whole idea with the Change Loki scene, where Iruma seems to be becoming more demon like as the series goes on.
So honestly if this is the case, then we need to think about how Iruma ended up being raised by those shitty arse parents in the human world and not Derkila assuming Derkila is his father. Additionally, I would like to actually see the contract between Sullivan and Iruma's parents, because they could have sold Iruma when he was a baby with how money driven they are, so why wait until he was a teenager to do so? Not to mention how they even managed to pull off a summoning ritual to call someone so powerful like Sullivan in the first place, since humans are said to have no mana/magic? Plus, Sullivan himself is a little suspicious; not in an evil way, but he definitely knows that there's more to Iruma that he lets on and I would love to see how that played out.
Ok so just reread and started rewatching with the current release of S4 of the anime and had some questions.
What does everyone think Iruma's relationship with Delkira is? We know that Delkira disappeared behind the door to another world and that Sullivan probably chose Iruma specifically to be his grandson. Reincarnation? Descendant?
Also technically Iruma as a human shouldn't be able to use magic, but he did during the 1st year welcome ceremony with the forbidden spell. The no tripping spell. I wonder how?
Anyways just thoughts. I would be curious to hear what everyone else thinks!