In my campaign setting beings summoned to the world from other planes are kind of trapped if they don't know Gate or Plane Shift. The region (planet) in question is so far removed from the established multiverse getting to and from it is nearly impossible if you don't already know how.

Jumping forward, a group of celestials (among other creatures) were summoned by accident all over the place. The one I want to focus on is an Astral Deva (taking a lot of inspiration from pathfinder and 3.5)

As the 3.5 and pathfinder Astral Deva can planeswalk (and the region it was summoned to is well beyond the reach of it's devoted deity) a dm friend of mine and I agreed it would likely have assessed the region before returning to it's court.

The problem then is that, It would have taken note of the evils (devils, demons, etc) of the region it came to and likely would have left to seek aid or report. If this is the case I'm unsure of what aid, if any whatever deity would grant (taking pathfinder and 3.5 into account) as the world is beyond the devotion of any known deity. My friend assumes it would have some form of pull due to an Astral Deva's rank but would be unlikely to return on it's own accord.

This is kind of the origin story for angels in my campaign setting (i know it's complex and roundabout). I'm open to criticisms and suggestions thus far.

Maybe they sent a message and were told to hold down the fort and await reinforcements.  Yet no reinforcements ever arrived, or were lost.  You could have them find the lost reinforcements or something, or they were even told that it is outside the realm of possibility to send much to them.  The planes are not in the proper alignment.

Are you then suggesting that the deva does in fact return, though without any aid. I had considered this but then I wondered how that deva might fair mentally over a few hundred years. It is after all well beyond the reach of it's own god, would it maybe go rogue?

I hope I don't sound dismissive, it took me a minute to decipher the comment. I am thankful for the thought.

Yeah, was typing in haste, apologies.  Some form of communication, not necessarily in physical form.  There could easily be a divine version of the message spell, but it could take a lot more energy to perform.  If they are somewhat removed from where their patron god is they may not be able to generate that power consistently, and continue messaging back and forth.

U mentioned they could be searching for the missing contingent sent to help, I meant the players.  The party could be trying to find the other angels.  There could be reasons that the astral deva cannot go search himself (drained of energy, sealing a demonic portal, et al).  

I wouldn't assume the angel would go rogue unless you mean go on a crusade against the evil in the world, not unless something was actively trying to corrupt it.

Hopefully this post is a little more coherent.

Thank you for the input, in regards to searching for a contingent, I hadn't planned on the players going and looking. This is more of an origin for how angels and aasimar came to this world in the first place. Since the players won't have access to gate or plane shift until fairly high levels it would make for a long off story. My payers in this setting right now aren't even to 4th level yet, and unfortunately have a habit of making less than wise decisions.

The deva might go on a crusade I guess, one of the other creatures summoned to this world is an Azata Ghaele (Pathfinder Bestiary pg. 25), who most certainly has begun doing just that.

Something that could be fun to play out is there is an uneasy peace between the Gaels and the deva, but though their end goals are the same the methods to achieve that could easily cause friction.  Make them the centerpiece for your lore.  The deva is more defensive wanting to wait for additional celestial assistance in laying claim to this particular plane for god, and good.  The ghaele is taking the fight to them, and stirring up trouble causing friction due to its actions.  

Perhaps their patron gods ordered them to work together (stranger things have happened right).  A little good cop, bad cop scenario, forced together by the department heads.  I would still say that for some mystical magical planar reason, that reinforcements are difficult to come by if not impossible.  Even reasons of the wars with the abyss have ramped up and they cant spare any attention to a backwaters planet that doesn't even offer worship to them.

Did you want the deva to have some impact on your main story?  What kind of impact?  Sometimes you can create the circumstances of your lore around the story you want to tell.

I had decided that the deva, ghael, and a few other unrelated celestials (unimportant to this topic) would be the world's first "gods". Or at least the first divine beings the people of the world would have encountered in over 600 years. They would be pseudo-deified and potentialy be the origins of the aasimar, azata, angels etc. that can rarely be found on that world today.

Over time a few heroic mortals would have eventually developed their own godsparks and become true gods of this world (over the next few centuries) making their divine rule obsolete but not entirely banishing them from memory. The Ghael is still pursuing her crusades whenever she wants, inadvertently starting paladin orders wherever she goes.

The deva, if left to it's own devices, was more nebulous, so I figured other experienced players might have good ideas for what would become of it. I kind of like the idea of it occasionally aiding the Ghael in her own pursuits (as a knight errant she was pretty much told it's her honor to uphold thing there).

i like that idea, semi/Divine/celestial of some sort, arriving on a plane, imposing themselves as gods, and then the people eventually becoming their own gods, its essentially what happens whenever a player hits lvl 20, there's a campaign in that idea of being the lowly mortal, who ascends to godhood, toppling the current religious regime, be they fair or foul, and the type of rule the instill, later campaigns events, and divine interventions influenced through any other campaign o ran through that plane....vestiges of the influence upon the fabric of reality. on top of weather or not, other people can also become deities or demi-gods/ saints/ etc. will someone that plays in a campaign a year from now, become the god of war to the initial characters god/ of _BLANK_ and how'd they interact during say a war of planes, or gods in plane. endless possibilities. *sigh*

It is a cool concept, and definitely something to wax poetically on, especially seeing as it was the end goal of most players of 4th edition (what with immortality being handed out at 30th level the way it was), but here it's more a testament to the surprising will of a rare few.

But I digress, much of the lore I am having issues with here is primarily about what happens with the deva, he shows up, then does he stay or go? If he stays does he send a message for reinforcements, if he goes does he petition for them? If his message or petitioning is heeded how many angels come, and what force would be sent, planetars, solars, empyreals, or simply a contingent of devas or battleforce angels, maybe Chalkyrdi or the like. On the other side of the coin what if no reinforcements come at all. What then does the deva do, does it simply help people best it can, does it join the Ghael in crusades, does it go rogue, or does it simply not care and bounce all together.

The answers to these questions will mold the lore of the angels in my world, how they came to be, and how aasimars by extension came to be.

How big of a demonic threat is there?  Were they trying to turn this world into a connection to the abyss or something similar?  If large scale they might send something on the order of a planetar to get things under control.  If something a little smaller maybe nothing at all.  The deva could be going about promoting peace like a monk traveling about preaching the good word.  If you want some event for the players have a relatively large number of weaker celestial come and upset the balance of power.  This could create tension with the New Gods you had mentioned.

If you are more trying to just build a backbone for the world I would go with the simpler no others showed up but the deva is going about being an emissary of goodness.  Would an Astral Deva help a human on the path to ascension?  If it was for the good of this world perhaps.  Even if their orders contradicted this they may have a change of heart after a few centuries on this planet.  If that was the case would the home office be very displeased with this turn of events and try to stop it?  Possibly, that is on how you think being on this planet would change them over time.

I dont feel like they would just abandon the world.  Even without assistance they would try to better world.

At first the threat is comparably minor, just as a small number of celestials were called in by accident so too were a small number of demons/devils. The difference between the two is that demons and evils can sometimes summon more of their kind or lessers. There is no super gigantic threat posed by fiends but they are ever-present, they cannot leave but they can bring corruption to themselves. Demonic cults and whatnot.

I had initially seen the deva as a form of missionary myself which made sense. As for the gods, they are aware of the Ghael and the Deva, some of them are even on good terms with them. They came first, they have an almost immortal breadth of knowledge and while they aren't stronger than them, most of the good and neutrally aligned gods see them with respect.

I feel the same about the Deva, your input has been very substantiating thus far HeroZero. I feel as the deva would not entirely abandon the people of this world, even if no help comes. I also assume that no deity would immediately send servants to watch over a world beyond their devotion. The deva is not powerful by themselves but enough to police minor threats. I feel it would try to make the world a better place any way it can, perhaps even mentoring the newly ascended.

As you said most of this is world-building lore. My campaign has many "moving parts" the world contains a number of intersing individuals and historical plot points for adventureers to explore, if and when they decide to do so. But say a player (a high level cleric for example) wants to use conjure celestial to summon an angel, how then would that angel react to being ripped from it's own portion of the multiverse and trapped here. Aasimar are another topic, being the children or descendants of celestial beings, they would be quite rare with only a single angelic being on all of the world, more specifically one who acts as a missionary.

I know this line of thinking is getting far more exasperating that it probably should, and I both thank you for your patience and apologize for my own indecisiveness.

I feel as though I've come to consensus.

Lore-wise the Deva spent some time crusading the planet and fighting the stronger demons/devils causing trouble, he then left to report to his deity about the his absence and the world plight. I feel he is sent back as a messenger, his petitions for greater aid dismissed due in part by the lack of devotion the people show and the distance and complexity of travel. The deva however cannot leave the world without aid, so take back to the planet with him the secret of creating angels. He gifts this summoning, conjuration knowledge to the Ghaele, but this cost him his ability to plane shift (reflecting a 5e devas inability to plane shift at will). Dis-ranked he becomes and angelic missionary and pilgrim, spreading a positive message and aiding the Ghaele when he can.

The Ghaele, whose own summoned allies have sided with the Elf Queen, accepts this gift and creates the first Battleforce angels (the only angels explicitly unrelated to any main series god). Aasimar are born tot he world with the blood of celestials in their veins, Some are born of an ancestors union with the messenger deva, some have the Ghaele, some have the Bralani or Lillend or another azata.

read my signature if you want a god

maybe he could be a servant of bahamut (god of good dragons). after all the githyanki ride red dragons (evil dragons) and bahamut HATES tiamat so killing all those red dragons hast to be done by someone