As all rogues, Xishiori had to master the art of a poker face. Not just any old neutral expression – one of absolute innocence. Theft worked better that way, and a sufficiently calm demeanor could spare you from a couple enraged guards or the prison.
This, obviously, had uses outside of her line of work. As Mirae had found out, when most of an inn's drinks had been stolen, and Xishiori was just under the window with a dazed look on her face. When the priestess had finally managed to extract a story from the rogue, she wouldn't have believed her capable of the theft.
She had to take that back when Xishiori stumbled into the Temple later on begging for a hangover cure.