So since the new season has been going full swing and I can't exactly get the manga on my kindle (not available), I have read several chapters online and am pretty caught up.
So... I started questioning a few things regarding Iruma. My belief based on what I have watched and read is that Iruma is the Demon King reincarnated as a Human/half-demon and that Sullivan is in on it.
The questions that brought me to this are as follows:
Why did Sullivan adopt him as his grandson? *Opera even asked this question in the first episode*
How and why was Iruma able to cast the forbidden spell on the first day of school?
Why out of everyone who put their hand inside the Rank Owl is he the one who got the "Ring of Solomon/Ring of Gluttony"?
During the battler party, why did he sprout demon wings when he cast Pandoraca?
How did Ali's spell to make Iruma "a bad boy" work? *Ali had stated when talking to Iruma that 'Spells that change a person personality don't work unless they have an innate desire to take on that spell.'*
When The Misfit Class gained The Royal One, how did Iruma know where to go to find the throne?
Why is it that so many demons who have seen the demon king, say how much Iruma looks and acts like Derkila?
During the Music Festival, why did Amduscias state "Your heart sounds JUST like his"?
Why did Amduscias immediately think that "Sullivan's Grandson" was Derukira's son?
Now one of my theories based on these questions is this: Sullivan's magic specialty is Time and Space. *I have seen plenty of anime/read plenty of manga/light novels to know that time and space magic can change a person's fate (ex: Misfit of Demon Lord Acadamy)*
With Sullivan being known to hold the demon king in higher esteem than just about anyone else in the series, could he have not used his magic to give the demon king a way to alleviate his boredom by altering time? Plus with the fact that he immediately took to Iruma as if he was his actual child, makes it even more possible he used his magic to turn the demon king's clock back to him being a baby and it also shows how Iruma's parents could be so cruel to their "child," especially if he just happened to be dropped off at his doorstep.
In conclusion, my final theory is this: The Demon King Derkila was bored of dealing with the 13 Crown Dinners as wells as the 13 Crowns and with the help of Sullivan either turned his internal clock back to being a baby and was dropped off at Iruma's "parents" home for them to raise or he split his soul into three pieces (the ring of gluttony, the plant in the harvest festival and Iruma) and reincarnated himself as a human/half-demon with sh**ty parents so that he would grow up strong enough so that when Sullivan came to get him when he was 14.
Of course, I'm only speculating on what I think is the true connection of Iruma and the demon king.
I'd love to hear everyone else's opinions.