When creating a faction, four pieces of information are needed. Public facts about the faction are what everyone knows; their asthetic, where they're often seen, whether they interact with other factions at all and so on. The secrets of the faction are the ultimate goal of the faction, and what sinister secret the faction is hiding. These can vary from illicit supernatural drug deals to bringing back the dead attempting to unleash a sealed god-like being. The setting is very flexible, so be as creative as you like.
Technology level: The setting's tech is around late Victorian/turn of the century era levels. If you want your faction to have something that doesn't fit this (say, a computer), that's cool, but in general stay about that level.
Supernatural Activity: The theme of the game is the Supernatural hiding in plain sight. Supernatural powers permeate the entire city, but most of the populace's only open interaction with them would be the Six Spires. Feel free to have lots of supernatural activity, but as a rule it should part of the secret information, and its visible effects should be in the public information. Some things may simply be strange, but be treated as the way things are. As above, the setting is very flexible so have fun.
Information required for each faction.
Public:
Faction Description: How does the rest of the city see the Faction? What is it's public face? What would be a good midlevel position for a player to start out as?
Faction Members: Who makes up this faction? Why might someone join it?
Private:
The Goal of the Faction: If the Faction gets its way, what will happen? If you want to leave this a bit flexible and leave it up to the GM, for instance if the factions aim involves one of the Six, that's fine but give a rough idea.
The Faction's Horrible Secret: This game is aimed at somewhat surrealist horror, so feel free to go wild with this. As a rule, the Secret is what the faction is doing now to work towards their goals, although obviously their goals can be horrifying as well. As a rule, be creative, but also be aware that I may veto the secret if I don't fit the tone of the game (no non-consensual sexual stuff).
The Public information should be put up in the Factions forum, and both the private and the public information should be sent to the GM.
Example Faction: The Counterwise Docks and Warehouses
Public Information: The Counterwise Docks are the main port for the Sixfold City. For the most part, they are as one might expect for a dock; ships coming and going, burly dockhands and cranes moving cargo into the warehouses.
The Docks are managed by the Dock Master, a polite elderly gentleman with a strong old fashioned streak. The Dockworkers have a certain standard they are expected to live up to; a sailor cussing at this port will be swiftly shushed, should the Dock Master hear and begin a quiet but compelling lecture.
One curiosity of the docks is Warehouse 16. The largest of the warehouses, it is known for being able to store fresh produce for far longer than one might expect; summer fruits are brought out of it in winter as fresh as when they were first picked.
Members: Most of the Dock workers are hired hands and accountants, here for a paycheck. A good starting player position might be as a manager of one of the warehouses.
Secret information: The Dock Master is far older than he appears, having been here before the Six founded the city, and is not happy about these interlopers. Unable to challenge them directly, he has instead spent many years experimenting with time, with the aim of ultimately reversing it and returning to a time before the Six arrived, to prevent the city ever being founded. The results of his experiments are kept below Warehouse 16; the Younger-Than-Themselves, shambling immortals who are taken out to sea and dumped when they are no longer needed.