World Symphony

When the Grand Empire of Karadia expanded its borders to Telya, it came into contact with the followers of Khardism - a local monotheistic religion. It was a rather complicated relationship. When the Twilight War shattered the imperial power, the previously mostly independent Holy League had a perfect occasion to expand. Today majority of the continent is overshadowed by its power.
What's more, there are now some Lost Lands in Telya. There are much less of them than in the Karadia, but there are still some. The is a connection between all Lost Lands, so if one were to enter them in Karadia and was ready for an extremely long and arduous travel, they could reach Telya that way. Naturally, this means that the forces of the khardic monotheist god - the Overtyrant - are at least technically capable of reaching all the way to the Grand Empire.
They do that rarely, and typically while pursuing the forces of the Umbral Bond. They are much more common in the northern Telya, where the shattering was more pronounced yet the close ties to the imperial gods mean that the legions of the World Symphony have a lot of work to do. While the Overtyrant is a benevolent god, he also refuses to accept the existence of other deities, which often changes the relationship there between imperial cult followers, the fallen and the World Symphony into a melee-a-trois, although with the Symphony waging a war that's much more civilized when it's done against the imperials.
World Symphony is a threat that many of the imperials from Karadia aren't even aware of, maybe save for Vestiria when one can find a sizable khardic community. They are incredibly dangerous, even in the lands under the imperial cosmology which significantly weakens them. They are also incredibly insane - their equivalent of paladins is quite likely to be wearing a skin of their enemies or carry other gruesome trophies (to terrify their enemies), they use what's essentially 'holy occultism' (which corrupts them like the Ancients of the Umbral Bond do, but in reverse) and might just end up eating your body in a form of sacrifice to Overtyrant (if you are a seriously bad and powerful guy and they consider you a good enough sacrifice).
In the end, the biggest problem with the World Symphony's problem is that when they actually appear anywhere in the Empire, they tend to so as an outside context problem that nobody's really prepared for. They go through a section of the Lost Lands, ripping and tearing everything evil that they run into, and retreat before something in the area manages to figure out how to respond to that. They are also cases of them appearing in much smaller numbers, as a bit of a raiding parties (often of older warriors of faith, that are simply looking for a nice place to die in gloriously).

Structure

Greatly varied. The Holy League has several member-states, each with their own traditions, including even the certain organizational elements of religion (and the Overtyrant doesn't seem to mind). The same can be said about the various holy orders that tend to contribute the mortal side of the World Symphony's forces.

Military

The World Symphony's armies are divided into two parts. First are the mortal adherents of that religion, typically militant to an extreme and capable of using often insanely powerful miracles in combat. They are mostly khardic beastkin (unless they are regional converts), who has mastered the use of both their organized, calm and precise human side and the instinctual, wrathful and powerful animal side. They can give in the second half whenever they want, and when they do, they remain cognizant enough to temper their rage and ferocity with intelligence.
What's more, they aren't barbarians - their society is one which has its own share of refined culture, and it shows. Their armors are of high quality and their weapon is always properly blessed, meaning that even the spear of some village watchman will deal additional damages to anything supernatural which isn't of khardic origin. That alone makes them dangerous, and often completely unexpectedly.
The khardics field disciplined armies who know how to fight in formation and will maintain it for as long as needed. Then, when the enemy is broken, they will break the formation and give in to their beasts to begin slaughter that will mentally scar the survivors for many years. And then, when some of the enemies will reorganize or the enemy reinforcements will arrive, they will quickly calm themselves and return to a formation.
Overseers are the supernatural equivalent of daemons for the khardic religion. They are sorted into seventeen hierarchies with different types of abilities: seven for the Seven Primeval Virtues, seven for the Seven Harmonies of Character, and three for the Three Pillars of Faith, with the ones belonging to the pillars being the strongest ones by far. They are all known, however, for the fact that however they look (and they often look pretty weird), they will cause sanity damage to anything in the vicinity, depending on the actual number of sins, disharmonies and anathema (the counterparts to the Primeval Virtues, Harmonies of Character and Pillars of Faith) that the onlookers committed.
Like in case of other monotheism, their god have went for quality instead of quantity. It's rare to see more than a single overseer anywhere, but if you are evil and you see it, you are pretty much screwed up. This is especially sure if you end up running into an archoverseer, because that's a threat that requires a Chosen One with an entire entourage to have any hope of stopping, much less defeating.