(363 words. Billie/Daud-ish but also Billie/Deirdre.
Further prompted by the comment "a small rat comes and ties a red cord around your wrist". Because if anywhere is going to have rat-based soulmate myths, it's definitely Dunwall.)
A rat bit Billie on the wrist when she was little, hard enough to bleed and puff up red and angry and leave behind a scar when the fever finally faded away.
In the slums, they used to say rats walked in the Void and could see things invisible to all other creatures, that they drew the important connections between people, tied the threads that pulled one soul to another.
Even as a kid she had trouble believing that one. It was only a story, one for tired, desperate parents to quiet their crying children. She doubted if anyone ever had to explain to wealthy brats why it wasn't so terrible that rats and fleas chewed them up while they slept.
But Deirdre had always liked the idea, even though their scars didn't match like they were meant to. Hers was a notch in the ear gouged out by tiny teeth, and she said the rats must have known how much she would love hearing her Billie's sweet voice to connect them that way instead.
Blood poured from Deirdre's ears when she died.
Billie always read her letters out loud before she dropped them in the river, just in case there truly was a rat scurrying through the Void to bring her words to Deirdre's spirit.
With the gloves he always wore, it took her some time to notice Daud's scar, an old bite wound in damn near the same place as her own. Too ridiculous to even mention once she did, and the plague soon stopped any talk of rats bringing anything other than death. But smuggled below decks on the last ship out of Dunwall, anger fading as the guilt lingered on, Billie rubbed her wrist and wondered if they told the same stories to kids getting torn up in the slums across Serkonos, wondered if his had been as painful as hers at the time.
She should have known it could never have been anyone sweet as Deirdre for her. Something that burned and bled like that, nearly killed her before she grit her teeth and pulled through it stronger, could only have been connecting her to someone like Daud.