Oslaka is a Geisterdame whom Othar Tryggvassen, Gentleman Adventurer encounters during his Twitter-based adventures. They meet in Paris after her charred corpse is discovered in the aftermath of a fire, and she is subsequently revived by the Master of Paris. Othar's investigations show that Oslaka somehow ended up alone in the city and had been hiding out underground for at least six years, covertly scavenging for food and supplies. Her revival is supposedly temporary, but Othar helps her flee Paris, and she survives past her assigned expiration date. They eventually end up alone together on a small island in the North Sea where they live connubially for thirty-odd years until she dies peacefully in her sleep. Othar returns to the mainland to discover that Europa is a very changed place. He eventually finds himself thrust back in time, at least mentally, and considers going back to Paris to find Oslaka again, but following certain half-remembered instructions, instead sets off to Mechanicsburg..
Due to the temporal and mental instability in Othar's story, there is considerable question about whether Oslaka actually ever existed. (Or if she once did, if she is now again/still alive.) However, it's been confirmed in-comic he learned to speak the Geisters' language somewhere, and his account of how she survived in Paris, and how she reacts to the outside world sheds some interesting light on Geisterdamen psychology: for example, she takes the opportunity of a visit to Notre Dame to silently pray, while the sight of the rising moon terrifies her. She also indicates that she does not consider herself required to re-join her sisters in their service, and willingly goes off to live with Othar as described above. And more domestically, she knows how to make a pretty tasty rat stew.
Following his Mechanicsburg adventures, Othar does return to a Colette-ruled Paris in an attempt to find her, but instead encounters her fellow Geister Eotain.