"It is the 41st millennium. The shrine maiden of girlkind has sat on her turtle throne for the last 10,000 years, protecting the borders of the Imperium from Youkai incursions originating within the Gap of Terror. Within the borders, the loyal members of the Adeptus Divanicus, or Space Fairies, try to fight the only way they know how through sheer weight of numbers. Whole planets have been turned over to the production of danmaku, known as Curtain Worlds, that supply the soldiers with all important wargear.
Girlkind faces danger at every corner of the known galaxy. In their world ships, the mysterious and illusive vampires cling to what remains of their once powerful empire. Elsewhere, hordes of Oni gather in great drunken warbands, known as Brawls, descending on planets, drinking all alcohol and leaving a dry husk behind. A terrible fate for those stricken, for alcohol is the lifeblood of the sprawling Imperium.
From within the Gap of Terror, traitorous legions of fairies lead by champions of the four Gap Gods, storm the walls of countless planets. Their ancient masters feeding of the different emotions of their victims; Yukari, the god of plots and hope. Yuuka, the god of anger and bloodshed. Eirin, the god of disease and stagnation. Yuyuko, the god of excess and perfection."
Hmm, about time I stopped before it becomes too long.
Edit: I was encouraged. Foolish mortals, now you have to read my drivel.
The Curtain Worlds are protected by the Adeptus Magicus, a private army of mages who spend their time "borrowing" artefacts from other factions with the intent of returning them after they've all past away.
Other than the Adeptus Divanicus is the Imperial Puppets, or Astra Pupa. Lead by brave puppet masters, these mindless dolls are loaded with explosives to charge into enemy formations.
Among other factions, there exists the Kappa. A young faction, their technology already rivals that of the Imperium and their shy nature encourages other factions to join them.
From beyond the known galaxy comes the Tewinids. An seemingly endless swarm of rabbits that devour all vegetable matter, pilfer money, scam citizens and leave planets covered in sticky mochi.
Awakening from their ancient slumber, the long dormant buddists stir in their tombs. Lead by powerful nun mages, these beings seek to bring peace and unification to all the factions in the galaxy.
A splinter faction of the vampires, the Dark Vampires are well known for their lightning fast attacks, leaving little left standing after their powerful attacks. Their speed comes at a price, however, as what they have in speed they lack in defence. Raiding settlements, they take prisoners to satiate their blood thirst and are lead by crazy, reclusive masters.
Following their ancient gods, the traitorous members of the Moriya Shrine arrange their forces against the Imperium of Girlkind, seeking to steal worshippers from under the watchful eye of the God-Miku.
From within the Imperium, the ever watchful Tenkuition keeps a close eye on happening news, re-writing it as they see fit and distributing the Imperial Truth.
Uh... I can't think of anything else to cover. I'm not happy with all of it. I was thinking of writing Kanako and Suwako like the C'tan but Byakuren Hijiri and Myouren Temple became the Necrons.
I am also rather out of the loop with Touhou, and have not played any of the games after U.F.O. so the more recent characters I know very little about.