Okay, okay. My previous prediction was wrong, so I have another one. It's a very minor non-plot related spoiler for ch451.
So Sullivan's last (surprisingly for me) name is Samael (a fallen angel), and there's also Azazel, so what if we once get Derkila's second name revealed and it turns out to be Abaddon?
[ADDED the page in English and Japanese, since not all readers have noticed it]
Bottom-right corner, It's Samael Sullivan in Japanese version, so Samael is supposed to be his surname, though it's strange:
So I've been thinking about this bit in chapter 205:
(Spoilers for 205 and later!)
Some things we know about Derkila (a character who has been repeatedly, overtly paralleled with Iruma):
his request lead to blue flowers blooming on magma
he founded a new country without warning
he tried to channel a river back to his castle
he stopped a war by taking a hit from every side and allowing no one to be hurt
he wiped out an army overnight
These aren't all of what we know about him, but they're crucial, because we see these happen to Iruma.
Iruma praising Asmodeus' fire leads Azz to developing the fire flower 'Amaryllis' spell that we see during Heartbreaker - the manga even directly references Derkila's fire flower demand during this.
His Scala(?) test is all about founding a new country, with very little warning nor leadup (at least for Iruma).
As for the river (which we learn more about in later manga chapters), I think Poro-chan's river of sound at the end of the Music Festival is a deliberate homage to that. At the very least, I believe it counts as the 'river' for Iruma.
So notable points that we haven't seen are "stop a war by taking every hit" (worrying for Iruma, who both is still learning to not sacrifice himself but is also notable for constant dodging) and "wiped out an army overnight" (he's had a variety of successes but I don't think we've seen the true analogue for this yet).
I'm not thinking of shit, I JUST WANT KIRIO BACK IN THE MANGA BRO. For one of the main villains his onscreen time is like that for a side character instead of a main one just saying