Zashiki-warashi (座敷童/座敷童子) are a type of benevolent Japanese youkai originating in Iwate Prefecture. Inhabiting households, they are thought to bring good fortune to their residence and the family occupying it, and bad fortune should they leave. They must be cared for and raised properly and evenly, as one would a child, lest they be driven away. As a child-like youkai, they are prone to causing harmless mischief around the house, and typically have the appearance of a child in a kimono, with bobbed hair.
Zashiki-warashi in Touhou
In Wild and Horned Hermit, many of the Human Village's zashiki-warashi leave for the Outside World due to heavy demand, but soon return when they learn that the work there is part-time only and there's no real need for zashiki-warashi. While they're gone, Yukari Yakumo brings in foreign household spirits to replace them: hobgoblins.
Though they serve humans, Yukari reveals they are actually spies for youkai, with the purpose of watching over the Human Village, and later infiltrating the outside.
- Wikipedia entry for Zashiki-warashi