He probably is a loose cannon type, and was ostracized..because of the type of power he has, others probably didn't like the dude.
Why he was the one, to do the fake peace treaty ,because of the type of power he has, it's just enough..to tempt the regular citizens.
He's probably gonna give us some info on why The abyss. wants to invade the human world, what they get out of it.
Probably will end with him going to the abyss and consuming the king
The ostracized idea works for sure, I'm wondering if maybe Devour was somewhat ostracized at the beginning since technically it's power only comes from eating others (so like MC it would start as like a lvl 1 and grow stronger), and that gave them a connection?
Not saying Devour is friends with Neutralize, but maybe it didn't properly hate on him or something?

I'm a little confused sir Neutralize Nachal, you proposed the peace now you are saying not to accept it? Bro is a hurricane whatever he does
I'm kinda hoping this ends up being one of those situations where Neutralize and Devour were on friendly terms so Neutralize just kinda wanted the guy back, but now that he's having fun living as a 'human' with Maru maybe he's okay with being friendly with both Devour AND Maru and not fight.
Also maybe he wanted to bring Devour back because the only way Nachals disappear is if they are destroyed in the human world and he's worried? Speculating a lot over here, don't mind me