I'm a lot more dissatisfied with his arc than anything. It's a bunch of setup and teasers for a future eventual arc at the cost of this one having basically no pay off. I mean, I guess it might not be over. But I was hoping to see more of Iruma and the others mingling and getting social. Kalego's brother literally didn't explain anything and just gave the vague notion he's either his own player or working with the thunder prick. The thunder prick didn't do much, he stole some praise and fame but that literally can't pay off till later.
It also feels like so much of this was "tell don't show", which is really surprising for an artist drawn Manga. Like for example when the thunder prick stole the show, against everything that's been setup and has been shown of the 13 crowns and security thus far we've just supposed to accept that literally everyone with power in the underworld is that useless? Baal only actually got involved because he orchestrated the even. Then there was Iruma and Azz and that's it. Nothing from Azz's mom who's literally there as Iruma protector specifically and supposed to be always watching and supporting him? Or Ameri? Or Sullivan whose previously been shown to dunk on and humiliate everyone with ease (it's really weird that all the three greats did here was make everyone stop panicking). I mean the school's teachers do a better job at protecting attendants. I mean it's not like it's just the 13 crowns and security, almost every demon worth a Damn was in attendance here and that all just gave up at the sight of a stomach mouth? We're just supposed to buy that other than Iruma and Azz (Baal being in on it), everyone couldn't be bothered to do anything but protect themselves? Heck, thunder prick saved the deity who had her own security force (which realistically should have been strong enough to hold off even the likes of Sullivan as she was the only deity in attendance and for all whomever sent her knew she could have been ganged up on by all demons). The deities themselves were also a massive letdown (after we JUST got hype for them). I mean maybe she does something cool later or we learn something extra later, but as far as we got in this arc she was just a damsel in distress whose own bodyguards suck.
I'm just generally not digging the way this has played out. It feels more like the plot bending to the thunder pricks will because the author needs setup than an organic outcome. The older brother cutting off his entire revelation and not telling Kalego Iruma is a human over a PHONE CALL pretty accurately sums up my frustration. The brother either does not care about Iruma being human as much as he let's on or doesn't care about Kalego's well being (as I assume he was telling him not to associate with Iruma anymore because he didn't want him caught up in Iruna's messes) despite claiming to put his clans interests first. Why even start the conversation if one ring on the phone (could literally have spit out human and then answered on the second or third ring) will make you withhold the most crucial information? I can buy last chapter with Clara calling and Iruma changing the subject entirely, but the way it went down here is a bit too much to keep down.
In regards to the demons not acting up, you must not think of them as human characters. Demons are selfish at their core. They prioritize their own safety over others unless that person is deeply important to them. None of those present cared enough about the deity princess over their own well-being. Each one thought, "Someone else will handle it." And add in the Greats were likely still suppressing the magics of nearly everyone to prevent a mass panic of magical use. Think of the chaos yelling fire in a crowded building, now add in everyone using magic to attack the presumed fire and causing people to be hit in the friendly fire. The Greats stopped that, so no one could react even if they wanted to.
As for Henri's action with the second mouth, he is genuinely shocked. He never heard of that on the other Crown and it is a genuine surprise. And given how quickly Behelmot moved, that second or two of surprise is all he needed to get away. And by the time he was away, no one, except Iruma and the villains were in a position to intercede.
As for Narnia, this shows his own self-interest takes priority. Even while he cares for his brother, he cares about himself more. He cares about getting to his new position and seat over telling his brother one more thing. He lacks empathy for anything not helping him get to his ambition.
And remember, Kalego and Balam not that different. In the Walter Park event, once the mountain bull was teleported away, Kalego was like, "Well, not my problem now. Sucks to whoever deals with it next." It is only because Iruma summoned him did he work to take it down a second time. And Balam is like, "Well, sucks to be you trapped kids. I'm protecting Iruma first." Again, Iruma moving in first is what makes Balam save the kids. On their own, they would protect their students but that's it.