Vampire: The Masquerade
Seattle is a Camarilla city. During the events of the Second Anarch Revolt, the sect fortified the domain to prevent any incursions from the roving Anarch gangs. Petrodon used the city as his base for incursions into the Anarch Free State.  As a result of his influence, the local Camarilla was much more hostile to Anarchs than elsewhere, with radicals such as Malkavian Primogen Takuma Sononda actively hunting them down. While the Sabbat has attempted several times to take the city, they were always thwarted, thanks in part to the aid of a specialized group called the Crew.  In the local asylum, the Malkavians and Toreador keep Sabbat infiltrators imprisoned. 
Following the fall of the Anarch Free State, a group of Anarchs calling themselves the “Seattle Committee” have gathered in the city and try to rally support for the reclamation of their domain from the Cathayans. So far, only Bishop Cicatriz answered, providing them with weapons, financial support (and also an informer named Malloc, in the guise of an intelligence and communications specialist), while the Camarilla stood silent. Given it's geography, the Princes of Seattle and Portland must frequently ally together to ensure that the enforcement of the Traditions is effective in both of their domains.
Werewolf: The Apocalypse
Seattle is home to a large concentration of Bone Gnawers and Glass Walkers.  Garou of almost every tribe have found Seattle palatable enough for a city and thus have flocked there. Two Caerns exist, the Menagerie Caern in Discovery Park and the Little Water Caern at South Lake Union. Both are in the hands of Glass Walkers.  Next to the Garou, the city is also home to several Kinfolk families of the Corax.
One of the concerning developments of Seattle is the cooperation between spirits of the Weaver and the Wyrm, with Drones supporting wyrmish technology developments.  The city is also home to the western branch office of Pentex in the United States.
Mage: The Ascension
Seattle is a major stronghold for the Technocratic Union. One of the shipwrights for the Void Engineers’ s voidcrafts is located there and is home to multiple Technocratic Enlightened personell.  The Syndicate’s Special Projects Division used to entertain a liaison to Pentex there, but recently, it was attacked and everyone vanished. 
The Traditions also have outposts. One of them is the Bridge Troll cabal, who operates among the city’s homeless and maintain a sanctum beneath Aurora Bridge.  Urban shamans work with the City Father of Seattle and his various spirit servants and allies.
Wraith: The Oblivion
Changeling: The Dreaming
Seattle is part of the Kingdom of Pacifica. The criminal gang of the Boggan Finney Fallon, called the Worcester Knights, is also active in Seattle. The local mental institution is the workplace of one of Hippocrates’ Dream Warriors, called Doc Samhaintha, who works to save future Changelings from becoming Undone through modern psychiatry.