The following is based on quite a bit of supposition, and may be negated or outright changed later on.
Is Yrael with us or against us?
Yrael is pretty firmly in the 'with us' category. Because he has helped us in multiple engagements and widely agrees with our plans and goals. If not 100% on board with our methods.
I imagine it would take quite a lot (like him hearing about the wildfire we sat on) to put him in the 'against us' category.
The problem with Yrael
One problem is how unlikely he is to actually put himself beneath us in
a formal power structure. This is a problem. We simply do not know why exactly, and we should simply ask him because he is an Archon, so we can do that.
(assuming he even can while following the laws of Heaven.)
Like any other sentient being his loyalty always will be
conditional. The problem with this is that he is a lawful good outsider. Which mean he will likely cleave as closely as possible to the
ideal of loyalty.
This likely means that his loyalty can and likely always would be
explicitly conditional. Which is a big huge butt fuck problem when you are making an empire and one piece of your map says. "Not actually part of the empire but were besties really".**
**At least I assume this would be a problem.
Why stop at swearing himself to us?
So we have Yrael. Who can, and likely would agree to troop movements, educational and cultural exchange, information sharing, status reports, spymilling info sharing, ect, ect.
The problem is what he is not willing to share with us. Which is not a lot, but is probably
some things. Combined with him having to be 100% 'You are the best and will gladly march into hells gate with you' loyal to us to join the empire.
I am also fairly certain him swearing himself into our empire would be desertion and or treason of some kind.
Territory.
Archons are naturally disinterested in taking and holding territory in the prime material. Believing mortals can and should sort their own problems out. Having done some reading I am kind of impressed Azema got him to hold onto the city.
What I think we should do.
He can and will go out and conquer regions in an effort to stabilize them. Making them more difficult to conquer. I do not think this is a problem, because politically, socially, and economically we can crush anything less than a free city in less than an afternoon. This problem will get smaller as we expand.
Frankly I would be fine with taking the slow(est) route. Just stay allies with him and create progressively more and more inclusive and binding treaties as we grow to trust each other more. Its not like he would go back on his word or stir shit up against us (intentionally). Which is far
far better for our cause than most. This would likely take decades or centuries. But our diplomatic prowess and the nature of Archons would prevent it from devolving into a huge cluster fuck in the meantime.
As I was writing this something kind of struck me.
If he refuses to swear himself to us on the grounds of still being a ranking member of Heavens military... Thats kind of a huge opportunity.
Because if he is we already have a leg up on diplomancing one of the outermost planes. If heavens government works the way I think it does it also means we have a leg up on diplomancing the
entire plane.
If this does turn out to be the case I would recommend we learn as much as possible about Heavens political landscape and begin capitalizing on our alliance with whatever passes for a faction in the mounting Heavens.
If whoever Yrael works for considers his words their bonds we can
so use that.
Wow this ended up being a long one.
TLDR: Slow burn treaties with Archons until they withdraw or we absorb them through osmosis.
Edit: WOW this ended up being really long holy shit. I even cut out a lot of it. No more writing at 3:00 am for me jeeze.
Anyway. I theorize that Heaven in its entirety functions as one single government whos members all help each other to varying degrees based on geopolitics.. As well as all being part of the same gigantic army.